The classic party trick goes:
- Tape a plastic bag between two pages of a newspaper
- Conceal the bag as much as you can
- Get a cup of water
- Pour water into newspaper/plastic bag
It's at this point you pray your shoddily-constructed attempt at magic holds its, well, water. If this sounds like an average Saturday night out to you, why not add an extra special touch to your routine with a real paper cup that can hold water.
Instructables has all details on this origami marvel. It's a lot simpler than the magic trick, at least.
Paper cup, actually holds water [Instructables]