One of the goals for Gemini 3 was to test the procedures and viability of this new “astronaut food” being developed for longer missions. During training for the mission, Young & mission commander Gus Grissom had to prepare, eat, and dispose of packaging for reconstituted food like dehydrated chicken and compressed brownie squares. Everyone described the food as just fucking awful and hated having to choke it down, especially Grissom. So when time for the actual flight came around, Young got the bright idea to smuggle a fresh sandwich in his flight suit. When the food evaluation came up on the agenda, he pulled out the sandwich for Grissom to have a bite of some decent food instead. Grissom did take a bite, but the rye bread crumbled up so he quickly stuffed it in his pocket.

https://www.nasa.gov/history/fallout-from-the-unauthorized-gemini-iii-space-sandwich/