@ Mr Ross -- around here, that corrugated plastic sign stuff is called "Coroplast". It's handy.
@ Luke -- Might I suggest one or two of these? They're also sold in eg Staples / Office Max type stores, if you can't/won't wait for eBay or Amazon --> https://www.ebay.com/itm/122831738441 I have one, it's my third, actually -- I have the remnants of the two predecessors around for spare parts. (They were abused to pieces lol.) Don't get me wrong, they're dang sturdy -- I'm just overly demanding of them ;) An Internet friend of mine who lives in Washington State helped me put together a custom axle and some lawnmower wheels on mine, so that it actually has ground clearance. I take it on the local public transit system (I'm kind of rural, so it's a mixture of handicap vans and Chevy Sprinters and hotel-type shuttlebuses) when I go shopping, because it beats the absolute heck out of hauling 10 bags of groceries.
Recently, I found a little tub with a lid, at the local Wal-Mart, that I can bungee-cord on over top of the bin, and get even more capacity out of it. The bin itself (I'm not sure about the tub and I'm too lazy to go measure it right now... probably about fourteen inches by sixteen on the inside)) is about a sixteen-inch cube on the inside, unfolded -- it can fold flat, about three inches thick plus wheels and handle -- and they're generally rated to about seventy pounds capacity. (That's a lot of potatoes! or anything else, really... unless you're a traveling cinderblock salesman, lol) I can vouch for this being the actual capacity... fifteen old laptops in a stack is heavy enough to cause problems, as is adding a 25lb box of cat litter to the usual grocery payload... my particular example has a half-inch wooden dowel, wrapped in electrical tape, across the front handle at the inside top... it holds things together nicely ;)