I always just eat an orange before exercising, and then go home and make dinner so I don't need a post-workout snack. You can certainly carry around an orange, a banana, or some other piece of fruit without worrying about refrigeration. I see though that you want some protein.
Cheese is probably fine without refrigeration for 3 hours as well, especially if you wrap it up well or pack it in an insulated bag. I even think yogurt or a boiled egg would be fine in that amount of time, if properly wrapped. A measured portion of nuts might work too.
Working off a partial regain. Current weight: 173. Goals:
Make the best choice I can make, with every choice. Remember that the temptation in front of me is not the last of its kind that I will ever see; say "I'll pass today." Say "no!" to my whiny inner five-year-old.