I try not to accumulate too many recyclables, but there are some things that are great to save ....
I have a few on hand, year round, but tend to accumulate them coming into spring, to use for caterpillars (a project for "The Very Hungry Caterpillar") and other bugs, as well as planting trays to start seedlings.
I save these for organizing project materials and to use with paint - painting small wooden objects, etc. - to have as drying trays. If you use in a classroom, you can mark with permanent markers or labels if a craft is hard to get a name on - you'll be able to tell whose project is whose by the trays!
margarine, yogurt, other small containers
Use these as paint cups (snap lids on to keep paint between uses) or as cups to sort craft project pieces in. Use lids for paint trays or to keep beads from rolling around. Use for round shape stencils! Use entire container for individual modeling dough containers, for quiet play time.
toy catalogs, teacher supply catalogs
Great for cutting practice - kids want to cut something that is interesting to them - have them search out and cut, then collage, things they find interesting.
Use for any project that involves looking through a tube (binoculars, telescopes) or use mini cars and set up tunnels and inclines for cars to travel through.
More to come - ideas welcomed......