A big bag can be a shelter. Christmas tree disposal bags are approx. 72"x90" flat, about 4' on a side if you run a cord through it for a quick pup tent, big enough to shelter two adults. Not heavy-duty, but they only cost a buck in the dollar stores, or in the after-Christmas sales. Put one inside the other if you've got a spare.

ZiplockŪ Freezer Bags, esp in the gallon size, are handy for all sorts of things. They can separate gear, keep things dry, and carry water and collected foods.

Boil-in Bags/Cook-in Bags for cooking in. Once used, they can be used for other things, at your discretion. I've ordered Freezer Bag Cooking: Trail Food Made Simple by Sarah Kirkconnell from the library. Maybe even more options than I realize!

Sue