Whenever I buy a snack, for example, almonds, I weigh out and pre-package multiple snack size bags so I can just grab and go. Depending on the snack, I'll do 3-5 bags at a time. I'll throw one them in the car, purse, etc. When I'm out, I'll have something to keep me satisfied instead fast food.
Snack size bags are easier to take along instead of tupperware, but to be as eco-friendly as possible, I reuse the bags.