Thanks to Portland, Oregon-based company The Original Nomad, you're now able to add a hot tub to the list, as the firm has just launched a collapsible tub geared towards campers.
When in use, the 851 liter (225 gallon) hot tub measures 152 cm (60-in) in diameter at the top and 142 (56-in) in diameter at the bottom, with an overall height of 60 cm (24-in). It looks large enough to entertain a few very good friends at once.
The tub folds up into a cube measuring 38 x 38 x 15 cm (15 x 15 x 6 in) and weighs 20 kg (45 lb), including the frame and an optional heater coil that's used to warm the water. You'll also probably want a water pump, or else spend a while filling it with a bucket.