I also use zip-lock bags, the "storage" type; they are a bit more durable. However, I find no matter how careful you are, movement tends to cause small openings that allow water in.

My favorite solution is to put the bags into screw top plastic containers of the type that COSTCO uses for many of its products. You can also find similar screw top containers in many dollar stores. You can also re-cycle some from products bought at your local grocery store.

Downside is that they don't pack as compactly and add some weight.