My kids are in the same situation. In summer I pack food in a small insulated bag with an ice brick and it stays okay until after school.
DD has to eat in the car on the way to gym, by the time we drive there she only has a few minutes to get changed. She trains for two hours and I find a small snack is enough to keep her going, she is always ravenous at the end of training though.
Fruit - apples, banana, strawberries, chunks of pineapple.
Yoghurt - spooned into a wide mouthed small insulated thermos to keep cool
cheese cubes and crackers
fruit buns
dried fruit and/or nuts
sandwiches - I pack an extra when I pack lunch
DS has an hour to spare once we arrive at gym so he can eat then, he doesn't finish until 7.30 pm so he needs more "filling up" before hand.
left over pasta that I zap in the work microwave and then put in a thermos
Soup
Microwaved oats with a flask of milk
fruit
cheese, small tin of tuna and salad
sandwiches
fruit buns
dried fruit
Both ds and dd's coaches like the gymnasts to have had an afternoon snack, but they do request that it not contain too much sugar, gymmies on a sugar high are not a lot of fun
Not sure how far from gym you live, but if you have a fair commute a healthy snack stashed in the car to eat
after gym can save you from listening to cries of "I'm starving !!!" all the way home.