You could pack your own food but you it requires more prep work and the maintenance requirements (expiration dates, storage temperatures, etc.) are more involved than MRE's. MRE's are convenient but nutritionally they're pretty lousy. Yes, you will be alive but after eating them for a few days you'll probably be constipated and generally feel like crap. For my emergency kits I use a combination of MRE's, freezedried meals from Backpackers Pantry, and my own food stuffs like almond/peanut butter, raw nuts, wheat germ granola, powdered milk, dried fruit, fiber packets, miso soup, salmon jerky, coffee/tea, etc. If you own a food dehydrator you have even more do-it-yourself options.