Build a mini jump line with the pallets. Or if you are the proud owner of a snow skate, build a snowskate mini ramp out of snow with the support of pallets.
you could try to build a minisub, or if that's too dificult, just burn em up in a huge bonfire and dance around it buttnaked while spanking your monkey to the rythm of justin Bieber's song "baby baby"....
If they are in good condition then sell them. You can get good money for pallets then buy a Large radius thick gauge reasonably long piece of PVC pipe and you will be set