Orikaso is a line of super-cheap, incredibly durable, brilliantly conceived flat-pack plates, cups and bowls, created by Jay Cousins (here's his blog). They're made out of super-durable, long-lived, environmentally sound polypropylene. Folding them takes bare seconds, and once folded, they stay folded and are perfectly water-tight. They unfold in seconds, and are (theoretically — I haven't tested this) top-shelf dishwasher safe. My favorite piece is the cup, which has lots of grace-notes, like metric volume measurements on both side and imperial on the other, and a handle that's so clever I actually giggled the first time I used it. The whole thing is basically a magic-trick.
For years now, I've been looking for a collapsible travel-cup that can be used with an Aeropress (part of my quest for total hotel-room coffee independence) and now, at last, I've found one. I just made an Aeropress in the Orikaso cup and it worked perfectly.
Did I mention that Orikaso is cheap? It's cheap: a plate/bowl/cup set is £1.99; a double-set (two plates, bowls and cups) is £2.99. You can get 'em in red, green or blue.
Every one of our suitcases is going to get a set of these zipped into the lining, just in case, and I'm going to add a cup to my backpack for everyday use.
Bowl and cup unfolded
Cup with Aeropress