Use a Flip Top Cap from a Vitamin Bottle over a plastic bag to seal dry ingredients. I have other flip top bottle and jar caps from parmesan cheese and coffee creamer that would probably work as well. From TipNut
I try to find uses for containers that seem too good to just throw away. These cleaned out coffee creamer bottles are perfect for day trips in a cooler because of their size, easy pour spout into sippy cups and tight fitting lid. And, I don't feel guilty tossing them after one use because I'll have more by our next trip.
Angry Bird Party Pig Bowling - Made from recycled Coffeemate Creamer Bottles