Help me prep food provisions for a sailing trip

I've done competitive heavy weather day-long races, but no overnighters. However, my experiences with that and longer backpacking trips may help. The lack of food prep and cooking makes it more challenging.
First, check for food allergies and preferences with the crew. Plan to send out a menu plan, but don't encourage editing or you'll never get past that stage. It's just to make sure everyone gets all their meals. Rely on the skipper to manage the review as that's who will make final decisions.
All meals should be packaged as 1-person/1-meal (like a MRE). Packaging needs to be waterproof, but think about where it goes after the meal.
Sandwiches and wraps don't age well, even in a cooler. Cold pizza can be a good option, if it's fresh. Plan for those for the first day and maybe the first breakfast, but eggs can be unappetizing after a day in storage, so you might want to think of an alternative like muffins. Day 2 and 3 lunch/dinner could be snack packs, like cheese/sausage /jerky/tuna packets /cracker/tortilla/dry fruit/nuts or similar. Buy quality and decent quantity. 2nd breakfast can be breakfast/energy bars or muffins. Get a variety, as these will also fill for between meals. The crew will burn a lot of calories, so get more than you think you need. Individual packs of nuts, fruit and other for snacks.
Bin everything by day/meal and mark the person's name on any special meals.
Juice boxes or cans for beverages. Good thermoses will keep hot drinks warm for 24hrs if they're not opened. Keep them in an insulated bin or cooler to reduce cooling. Having a coffee in the middle of the night or early in the morning can make a huge difference in morale. Use travel mugs for hot drinks. Caffeinated chews can be a good option after the coffee runs out.
Remember that most meals and drinks will be while sitting on the heeled deck or rail and need to be one-handed. After the first day everyone will likely be damp, tired and grumpy, so have good food and treats ready.
It should be a great experience. Have fun and safe journey!

if you ignore the sailing aspect of this, you've basically got a bunch of endurance athletes (just with a less-intensive activity than say running an ultramarathon). look into recommendations for food for groups of long distance bicycle riders and similar things.

get a big container of powdered Gatorade. staying hydrated will be very important, your crew may not notice how much they're sweating because they'll be wet anyways. the powdered form is great because you can mix it up at half or less of the normal concentration. if possible, you'd want everyone on the crew to have a Camelbak or something similar, so they can stay hydrated while keeping their hands free and without worrying about a water bottle falling off the boat.

most snack-type foods tend to be high-carb. make sure not to neglect protein. nuts like cashews are excellent for this. for the carb-heavy foods, you'll want slower-digesting carbs that will give sustained energy instead of a burst and a crash. eg, think Clif bars rather than Pringles.

for caffeine, I'd recommend some cold brew concentrate that doesn't need refrigeration, plus maybe some non-dairy creamer that is also fine without refrigeration. you can also get meal replacement / protein shakes containing caffeine - I drink one of these every morning because protein helps boost the effects of ADHD medication.

since you're not confident in the cooler, you can use it to keep things chilled, but avoid anything where food safety depends on the temperature staying low. food poisoning on a sailboat sounds like a special layer of hell.

No sandwich is going to last for more than a week and you're going to need some variety to keep morale up.
MREs are your best option, at least a few with chemical self heating will be nice, nothing beats a hot meal after a cold wet day.
Other than that, peanut butter, nutella, and oat bars are great and last forever.
Whe I go hiking I always carry a bag of nuts and dried fruits for snacking, not sure how well the fruits will stand the humidity of a catamaran but the nuts will be fine.
Edit: just saw it's 3 days, I misread it as 3 weeks.
Ignore the self heating MREs, it's overkill, just get some tortillas an stuff to fill them.

Jars of peanut butter and bread.

Don't prep sandwiches beforehand, at best they'll be soggy, at worst they will be bacteria-laden and you're going to be shitting liquid off the side of the boat. With no way of reliably keeping food, warming or cooking food, or preparing foods I would personally ditch the idea of having a fun variety of things. I would be looking at meal replacement shakes.

You could maybe do rolls with a hard salami and mustard.

For caffiene? I would take caffeine pills.

I would not eat two day old room temp breakfast tacos on a boat.

Depending on budget, freeze dried foods are good almost forever, and getting some freeze dried fruits can keep things interesting in a dietary sense.

Honestly food particularly designed for this might be best with all those restrictions. MREs as someone else suggested. Another possibility is just buy 3 days worth of something like Soylent (which they claim with a cursory google to be shelf stable at room temperature: https://soylent.com/pages/soylent-shelf-life). Maybe get some fiber supplements to along with that.

Or some kind of meal-replacement bar.

Sandwiches/wraps would not be a good idea. Too moist, unless you have a very broad definition of "sandwich" (are crackers and beef jerky sandwiches?). They'd grow bacteria to an unhealthy level per the FDA halfway through the first day and be unhealthy per normal people by the end of the first day.

If you have any dry storage areas near the bilge, or anywhere under the waterline basically, it can stay a couple degrees above the temperature of the water down there. When I briefly lived aboard a sailboat in early-June in BC, that was almost fridge temperature. I was able to store milk for a week. So, depending on the temperature of the water where you are, in conjunction with your cooler full of ice, your sandwiches might be fine for three days.

Anyway, I agree with pretty much everything people have said, other than trail mix since it'd be a pain to eat while sailing. Tortillas, peanut butter, jam, granola bars, protein bars, maybe pizza pops or samosas or jamaican beef patties or some other handheld product you can buy fully-cooked and frozen.

Edit: Hand pie. Hand pie is the word I was looking for.

I have experience backpacking, but it sounds like there may be some crossover.

You want foods that will keep at ambient temperature. Nuts and nut butters, dried fruits, hard breads, and individually packaged foods like jerky, cheese, and energy bars (string cheese doesn't need to be refrigerated). I've also had success bringing hard cheese wrapped in newspaper.

A popular food prep method for serious backpackers is something called "cold soaking." You get a mix of dehydrated grains, beans, and/or carbs, mix in some seasonings/flavors/additions, and store it in a Ziploc bag. When you're about ready to eat, you just add unheated water and let it soak for about 30 minutes. It makes cold, but hearty and nutritious, meal. There are tons of recipes online if you don't want to gamble with making your own.

For caffeine I would actually recommend chocolate covered coffee beans!

That sounds like a great adventure for you and your friends! A lot of great advice has been given already.

I think your main challenges will be: Food safety, 2) Food and liquid Intake; 3) Variety. Probably in that order of importance.

1) Food Safety
Hot and cold foods must be kept hot or cold. Otherwise, they will make you sick. And you really, really don't want to be sick on a sailing boat with a group of people. Once food is warming/cooling into the range of 40-140 °F, it cannot sit out for more than two hours.

You might be able to stretch this a bit, but I really wouldn't since you're on a boat. Proteins, moisture, and low-acid foods are more likely to quickly cause food poisoning. Especially on a boat, keeping things dry will be important. Even foods that wouldn't normally spoil quickly, like crackers or nuts, will go off quickly in a wet and humid environment.

Look for small packages of factory sealed / vacuum sealed, shelf-stable products. Like crackers, canned goods, powders, etc. Small packages will make sure that you won't compromise an entire supply of something if you only want a few units (i.e. many small packages of nuts vs. a big bag).

You can buy a cheap vacuum sealer to make individual, serving sized packets of shelf-stable foods like powders and dry goods. I think they sometimes sell FoodSaver sealers at Costco.

If you use MREs, I would get the ones with flameless heaters instead of the older style chemical flame blocks. They just seem like they would be safer on a boat. You don't want a live flame and fuel to accidentally pitch themselves onto the deck in rough waters.

2) Food and liquid Intake
You need to make sure that everyone will have enough food. Actively working on a boat will probably burn a lot of calories, as will trying to withstand the cold/humid/muggy environment. Apparently, the average sailor in the 1800s consumed up to 4,000 calories per day. A current US solider is expected to consume around 3,700 calories per day. Those numbers are a bit high, obviously. But remember to aim for something more than the 2,000 calories per day average.

You don't really talk about drinking liquids. But those are equally important. Men doing hard, athletic work should consume about 5.7 liters per day. Usually, some of that will come inside of foods. But that's going to be less likely if you're eating a lot of dry foods. Also, a lot of the foods that will be safe to keep around are high in salt, so you'll need to compensate by drinking more liquid.

Keeping everyone well fed and watered will help to improve morale, safety, and concentration. You're more likely to make mistakes when dehydrated and underfed.

3) Variety
I agree with a lot of the other posts here already. Commercial camping-style MREs would be a good way to add variety. And they're shelf-stable and pre-portioned. It depends on the size of your crew and your budget. If you're on a budget, I would aim for at least one MRE-style meal per day per crew member. They will boost morale and give people something to look forward to.

For the rest, the easiest thing to do would be to get a variety of carbohydrates and proteins you could mix and match. For example, crackers+tuna spread, melba toast+peanut butter, canned pasta salad+white bread, canned chili+pouch of shelf-stable prepared rice.

Keep a selection of single serving snacks around as well. For example, small packages of nuts, shelf-stable pudding cups, little boxes of sugary cereal, beef jerky, M&Ms or similar chocolate. Stuff you can just tip into your mouth directly from the package if you need to would be ideal.

Keep some options for flavouring and fortifying water around too. For example, Cup of Soup powder packets, instant iced tea powder, pre-sweetened Kool-Aid powder, full-fat milk powder, isotonic drink powder.

To save money, you could buy some of this in bulk, then split it into smaller packages, as long as those packages are also water-tight (e.g. Ziploc bags, vacuum sealer bags). Smaller packages will help keep things dry and easier to handle. It would be horrible if, for example, somebody accidentally soaked the only can of instant coffee on board 12 hours into the first day.

Hardtack, salt pork, and oranges. Live like a pirate! At least buy enough to throw on top of the real food in the cooler, give everyone a scare.