Large plastic jar lids can be used for wheels by hot gluing them to the servo horns.
Why glue them?
Position the servo horn (the round one is best) in the center of the lid, mark the holes (2 to 4), drill or punch them out, then use a few small screws (or small nuts/bolts) to hold them in place. Much more secure and easier maintenance (plus you can re-use the servo and horn later).
Hot glue is generally stronger than the servo shaft, and can actually be carefully peeled/removed from the servo horn if needed. The only real extra thing that needs to be done id drill a small hole in the center of the jar lid for the servo horn screw and the slight bump that might be at the servo horn screw hole. The Below bad video shows the setup with jar lids hot glued to servo horns.