Well the pilots/rio's that i worked with flying F4 phantoms and F18's would take all kinds of stuff to snack on, and during the over seas ferry flights (Beaufort S.C. to Iwakuni Japan, 2 tours, and 1 tour to Yeachon Korea) the cockpit's had no room to spare.
Fruit and raw veggies (carrots, celery, radishes, cauliflower, ect..) seemed to be the biggest snack foods.
MRE's when they first came out had a pork patty meal, thing looked like a dogg turd, that they had to discontinue because when pilots would eat it, it caused so much gas in the pilots that they'd get a form of the bends when they went up to altitude.
As for taking a leak, we had what they called "piddle packs" they were heavy duty clear document bags (zip lock bags) that had a compressed dry sponge in them. Pee into bag, sponge soaks up pee, seal, throw in trash after landing.