There was a time when I I scoffed at my mom for washing and reusing her Ziplock bags (and her tin foil). I mean, why in the world would you bother with the effort when you could buy more for so cheap?
Then I was introduced to the real world of a newly-wed, one income budget and suddenly I wondered why in the world anyone would throw away a Ziplock bag after one use. In my mind, it's almost like throwing away tupperware. Now, I salvage every freezer bag I can, with the exception of those used for raw meat.
It's not much of a hastle to rinse/wash them out when I wash the dishes, and I just drape them over the other dishes on my dish drain and they usually dry out within a day or two. I often use bags to store baked goods in the freezer. Some of them don't really need to be washed as I'll just be using them for the same purpose again, so I fold them up and leave them in the freezer door for next time (thanks to Crystal's suggestion). I often just fold used tin foil up and put it back in the cabinet where I store the roll of foil so I remember to use it if there's a piece the right size.
So, what about you--do you save your freezer bags and/or tin foil?