Laurs:
I think the solution to your problem lies in the kind of accommodations you have on hand:
Ultra-plush luxury (access to fridge and microwave):
If you're looking for something healthy and cooked, what about frozen veggies / fruit? All the health, but the veggies are already cooked (avoiding the raw food allergy). I have an SM friend who loves to keep frozen strawberries on hand, because they pack a nice healthy boost of energy, and she gets a bit of a cool snack; it's almost like having sorbet on hand. The other food to try might be microwavable popcorn- without butter it's still in the healthy arena. You can even get them in the single serving packs now.
Some luxury (access to a microwave):
The microwaveable popcorn is still definitely possible, as well as pretzels or animal crackers. They list a little more to the junk food side of things, but if you eat them in small quantities it's not too bad. You can still go for the frozen veggies if you plan ahead and pack them into a cooler with an ice pack (they can even work as the ice pack for your dinner....)
No luxury (no access to kitchen amenities):
When you get down to this level, it's really all in the planning. But that's what stage managers are best at, right? Organize yourself so that you've got a cooler packed with all of your goodies the night before. Frozen veggies, licorice whips, animal crackers, pretzels, pre-popped popcorn (the stuff they sell at the grocery store in the chip aisle...) or any other snack can all get loaded into a bag or cooler for the day. Make sure to bring along a liter or liter and a half bottle of water so that you don't get dehydrated- and also to wash off hands as needed!
Good luck