Lost Cooler from truck

After I packed my truck up, I looked around for more stuff to haul to Nevada and I added a large cooler. While driving around town, I lost the cooler it flew out from under the tarp and landed in the road.I stopped went back, got the cooler, cant figure out where the lid went because its gone. The tarp was still in place, so how did the cooler fly under it and out? will have to reorganize the packing situation before the haul to Nevada. Its like the 5th repacking of the truck since I got everything out of my storage unit on the 29th of May.