Expect a zit to break out on your forehead before the bus is 5 miles from home.
Expect the corps you're touring with to be eating steak when your corps is having "tuna surprise" night.
Expect McDonald's to taste like something Rachael Ray just made on her TV show.
Expect 28 years later (for me, anyway) to dream you can't remember the drill or music just as the corps is stepping off at prelims, and waking up in a sweat.
As for hydration, hopefully things have improved since the 70's as far as corps providing water and gator-ade type liquids. DON'T dip your cup in the big cooler, or drink from a cooler that other's have dunked their hands in. I saw an entire corps come down with strep throat because of this.
Not just corps members suffer from injuries on tour. Anyone remember George Zingali on crutches after one of his typical jubilation dances during a performance?
As the rule sheet used to admonish us every year, "TOLERATE, TOLERATE, TOLERATE"
You aren't on a Disney vacation. Think of it as a reality show where your "tribe" is every body else in your corps. You'll laugh, sweat, sleep, shower, suffer, and anything else you can think of (or not think of) together, and you'll make lifelong friends.
GOOD LUCK!