You know all those containers that contain items that you buy at the Big Box Warehouses? Why not get a little more use out of them? I have taken a few good plastic containers, cleaned them out and re-appropriated them to hold my son's toys. They could easily be used to house craft stuff or baking supplies or something as well.
First up I have a Tide Stain Release container. It is currently holding airplanes, dump trucks, and other small toys.
Next, I took an M&M cookie container (I bought the cookies on a "weak will" day...) and used it house some blocks. This could have easily been used for many different little items as well. What I like most about both of these containers is that you can see what is inside them because they are translucent/transparent.
I don't recommend keeping every single container you come upon. Those old Parkay containers, while they could be easily used for leftovers, confuse the heck out of someone trying to find butter in your fridge...Just my opinion though...if you wanna be super Green, then save as many containers as you can. Remember you can recycle a number of the plastic ones too, though...