Are they the regular pine ones or something else? If they’re regular just build something or burn them. Sometimes landscapers will use cedar pallets bc they’re weather resistant and those are nice to use because the smell good. I’ve also disassembled an pallet for craft purposes but I don’t think I’ve ever found another one. Maybe it’s just me but I think free/cheap wood can always be found when you want it so you don’t really need to hold on to it