Unique things to do in Las Vegas? (and Los Angeles)

My parents live in Los Angeles so I'm there often, but I feel like I've always done the big things that everyone's done (Hollywood Sign, Disneyland/Universal, Sunset Blvd (not worth it imo)) and eaten the popular foods (Leo's Tacos, Din Tai Fung, etc) so I'm wondering what other things I can do the next time I'm out there! I'm going out there for a bachelor party with a couple of friends in May, if that helps :)

A similar thing with Vegas, we'll be stopping by there for a couple of days after LA, and I know of all the popular things to do, mainly some gambling, buffets and shows, but is there anything outside of that that are considered -must do's- that we could check out?