This has probably been beaten to death but the advantage to the sand is if you encounter snow/ice and are stuck, the sand can be used for traction under the wheels.
My 2 cents: Put it in those large Rubbermaid containers we use at home here for storing old shoes or whatever. They have covers, are rectangular and you can use a ratcheting strap to hold them in place against the front of the bed.
Truth is, I don't use anything. Up here in the northeast corner we just accept the slippin' and slidin' as part of our winter dance.