More to the point for Guam and similar locations, canned and non-perishable food can are probably around and more can be airlifted in to get people through it. It was pretty much the standard back in the day.

The diet in Guam is already heavily dependent on shelf stable foods. I know this from personal experience but theres a surprising (to me) amount of research on it as well (c.v., https://www.guampedia.com/health-consequences-of-modern-diet...). However, it is worth noting that food on a military installation =/= food nearby, for many obvious and non obsvious reasons.