If you're going camping, or just want to cool a small room down without running the actual air conditioner, this DIY portable unit can get the job done.
We're no strangers to DIY air-conditioning systems, but I really like this one for its portability. You'll need to attach a PC fan to the top of a large protein shake container, then cut a hole in the side of the canister and insert a portion of a water bottle to direct the cold air into your room. Then, strap a battery to the side of the unit, wire up the fan, and put some ice packs inside.
The fan will suck in warm air, cool it over the ice, and blow the cooled air out of the side. If you don't have ice handy, just pouring some cold water in the container would create an evaporative cooling effect to achieve basically the same result. It's not going to cool an entire house, but it's pretty simple to build, and should at least keep a tent comfortable.
Cold Air Fan from Reused Plastic Bottles [Instructables]