Round Robbin - works best with 4-5 people. One person fires up a joint/blunt, takes a hit, then passes it. This person has to hold his hit in untill the joint makes a complete circle and comes back to him. Everyone in the circle does this so you end up with all but one person holding their breath for the whole session.

You get pretty high from holding the hits, but you also get light-headed from holding your breath for the better part of 10 mins. We usually do this when we are low on bud and want to get the highest on a small amount of weed.