Just wanted to add that hydration is as important as the food they put in their tummies. Since we're at 6800 ft., it is very important to make sure the girls drink quite a bit before the meet(yeah, then the whole issue of multiple potty breaks!) and get some water during the meet. I would say stay away from the "sports" drinks like Gatorade. They are loaded with sugar and are meant more for atheletes who are in constant motion--runners, soccer, basketball etc. The best drink is plain water, but most kids get tired of it quickly. Try adding a slice or 2 of lemon or lime---will give it some flavor. I've also caved and put in powdered Crystal Light mix(artificial sweeteners). As long as that will get her to drink it. Once they complain they're thirsty, they are already very mildly dehydrated.
As for food, beef jerkey in the gym bag seems to be the snack of choice. I have found out that meets like the school cafeteria is a time for swapping snacks. What you may pack as a nice wholesome snack may end up being eaten by a teammate. If we have a drive of over an hour and then the girls have the traditional warm up, I usually throw in a Lunchable. At least she can nibble the crackers, meat etc. Usually she eats on the light side the day of a meet and they are all famished when the meet is over.