My son was lead soprano/trumpet with Carolina Crown in 1999 and Cadets in 2000-2003. They always had pretty good tour food at both corps usually with a hot meal at dinner and lots of cereal, sandwiches, pasta, and fruit at breakfast & lunch. Snack was usually the day's leftovers with a few extra snack goodies like hot dogs, cookies, pizza, etc. mixed in. Sometimes a visiting corps parent would pitch in a snack or two for the entire corps.
I do not know how any corps could afford fast food thses days, but I do remember in HS/college being able to eat a complete meal at McDonalds in the late 60's and early 70's for less than a dollar.