Bring a pillow. Fall asleep (or pretend to) until the last 15 minutes. Wake up, say "oh geez, better get cracking" and do some gibberish work. Turn it in a few minutes early.
Get a copy of the exam, run out screaming "Andre, Andre, I’ve got the secret documents!!"
If it is a math/science exam, answer in essay form. If it is long answer/essay form, answer with numbers and symbols. Be creative. Use the integral symbol.