The Eye of Hercules: This one actually fools people, but it's so simple that most people write it off. To make it look you're opening a beer with your eye, remove the bottle cap and set it gently on top of the beer. Get the attention of your mark, place the bottle in your eye socket, and turn the beer as you mime opening the bottle with your eye. Here's the kicker, though: as you do this, make a hissing "Ssssss" sound with your mouth. If you get the sound and acting right, you'll actually fool them!
The Overflow: This is a gag everyone falls for exactly once. Again, if you're the first one to perform it on someone, you can be the jerk he'll remember forever. Just tap your full beer on the mouth of his full one...giving it a good rap but not breaking anything, and in 10 seconds, his beer will be overflowing with foam.
The Levitation: This gag seems to impress the performer more than the audience. By sticking your finger on the top and side of an inverted bottle, you can lift it up. Try it!
Stealing the Dollar: Again, this one's an entry-level gag, but one that everyone loves to play. Set the dollar underneath an inverted beer bottle, and explain that the mark can keep the dollar if he can get out from underneath the bottle without letting it tip over. No touching the bottle, no use of anything else. Once they give up, show that by carefully rolling the bill, you can push the bottle off the edge, and get away scott free.