I have two track junk boxes; one for each car. I think they came from IKEA. They fit into the froot with space on top for a slab of beer, or a soft overnight duffel and a couple of jackets, whatever you need. They'd work as beer coolers if you take all the crap out, I suppose.
As with the Rennline thread, they tend to get covered with stickers at PCF meets, where you use them as markers for your spot in the pits. And your stuff doesn't get wet when it rains...