Here's a great tip I found on Instructables.com.

I usually have several bags of chips open from various parties, barbecues, etc. They're usually lying around with tape, paper clips, and other assorted things that do a very poor job of keeping the bag sealed.

This Instructable let's you seal a chip bag tightly, without using anything at all. Useful, clever, and worth clicking over to see.

Instructables Chip Bag Fold