Last trip, I just packed ham sandwiches and cookies in the carry bag. I feel like a high-schooler on a field trip, but I'm not paying $10+ for box of terrible

Last trip, I just packed ham sandwiches and cookies in the carry bag. I feel like a high-schooler on a field trip, but I'm not paying $10+ for box of terrible snacks. Also, never pay the First Class premium on UK railways: it's the same sort of terrible box you wouldn't buy for $10 on a plane, but the fare premium was £20 on the train I took (Swindon-Plymouth)