Not a "fighter" aircraft, but certainly a small cockpit... in the U-2, I don't have the luxury of eating a bunch of "normal" foods. I prepare a few bottles of protein meal replacement drinks. They work like a champ. I don't get too hungry, nor do I get too full. I can just sip on the throughout the flight, and maintain an even comfort level.

BTW, no crapping in the space suit is allowed.

As for urination,... well in the U-2, that's a whole other thread.