cardboard tubes + box = hours of fun! We pieced together TP and paper towel tubes. Used marbles. The kiddo loved it and even still pulls it out to roll the marbles into a dump truck. He wont' let me toss any cardboard tubes now.
Life size Lincoln Logs made out of pool noodles~ 15 pool noodles from the dollar store, cut in half, cut notches out easily, with scissors = hours and hours of fun playtime! These were my favorite toy as a kid, love the life size!
Igloos are cool. What kid hasn't wanted to build an igloo? You can easily build an milk jug igloo in your classroom with some planning, lots of milk jugs and hot glue. This could be a fun winter craft for the kids when it's too cold to go out.