Clarence Birdseye would disagree. If freezing and/or refrigeration isn't an option, use shelf-stable or canned vegetables. Nuts, dried grains & legumes, etc. are clearly not going to be an issue. IRL there would likely be a combination in use at schools (and I advocate prisons) in the US and other developed countries.

In other places, people eat rather well without various food preservative technologies, particularly if there's no meat or dairy to worry about.