Tabletop Towns is a firm I found on kickstarter. Here is a quick look at one of the newer ranges they stock 28mm cargo crates.
So this is how it starts just a flat bit of cardboard. Nearly 2 minutes later it looks like this.
With a 28mm mantic minatures next to it for size comparison. Despite being very thin cardboard the whole container feels fairly sturdy when put together a pack of these goes nicely together to add to already existing scenery. These little crates will be following me down to the Wargamers Against All Cancer twenty four hour charity event this weekend to get put out on a few boards.
If you swing by to the site be sure to check out the awesome castle.