Hi! I'm a Level 5 coach, and my girls always get a 10-minute "snack break" during their 4-hour workouts.
I do not question or criticize their choice of snacks, unless a parent or child asks me for input. I want them to "be kids" and swap their Goldfish crackers for Cheezits, etc. I also do not want them to develop body-image issues at the age of 8. So again, I do not comment on food or drink choices unless someone ASKS me.
That said, I recommend WATER as the beverage of choice. Sports drinks contain way too much sugar, which has no real nutritional value and just gives kids a temporary burst of energy, followed by a crash. If you want to make water more "fun," I recommend Smartwater, which contains the electrolytes found in Gatorade, but without the extra calories. Vitaminwater is also very popular with my gymnasts. I don't know much about this, but having some extra Vitamin C, etc., in the winter can't be all bad ... and Vitaminwater is low-calorie when compared to Gatorade, for example.
Although I don't tell them what to bring, many of my girls bring fresh fruit: strawberries, watermelon (even in the winter!), pineapple, apple slices, etc. I strongly endorse fruit, especially if you can add protein, such as apple slices with peanut butter.
Other snacks I recommend include almonds, yogurt, string cheese, granola bars that are low-fat and low-sugar, 1/2 a bagel with peanut butter, healthy trail mixes, raisins, etc.
Parents, please make sure your gymnasts are eating three meals a day, especially breakfast. They need the calories ... they're burning a TON during work-outs. But make sure they are getting those calories from meals rich in whole grains, high in protein, low in fat and sugar. (The worst "food" is non-diet soda and fast food, in my opinion. Try to limit those as much as possible).
Also, a great birthday treat: Angelfood cake topped with fresh strawberries!