
There are a wide variety of waterproofing systems out there, each with its pros and cons.
If
you want to do it on the cheap, you can double bag your gear in garbage
bags. Use bags marketed for yard waste, as they are heavier duty than
the regular ones. Tie each bag separately and then put them inside a
duffel bag or knapsack to protect the garbage bags. One small prick or
tear and the whole system will fail.