Bring back the old skool Risk, i remember (kinda) playing Risk on magic mushrooms several years ago. it must have taken us about 3 hours to just get the game set up and all the armies put on the board...
if you want to make it really interesting take an old cell phone and write on it armageddon. make 3 cards titled armageddon. and distrbute them randomy in the deck. Then if anyone collects all 3 in one game and hands them in. gets to drop the phone on the board all the pieces that fall off the board or fall over died in the nuclear winter to follow a planet killing asteroid hitting the earth