Wood desktop finishing question

I built a basic panel out of some boards left over from another project. I'd like to use this as a desktop surface just laid on top of some filing cabinets. I'm wondering what the best way to finish this would be? I don't think I want to paint and I'm ok with some light staining but I don't have any experience with sealing or whatever I would want to do to help preserve the surface. It would have typical office items on it (keyboard, mouse, monitor, paper, pens, etc.).