A few tips:
Don't show up naked. It's frowned upon to show up naked, although feel free to strip during the festivities.
As tempting as it is, don't pre-game by downing a bottle of Kraken. You want to have all of your inhibitions in place until the boss drops theirs.
Bring your cellphone. You can record incriminating video/audio and take photos of anyone you may need to extort in the future.
Have a written contract prepared regarding any important pay raises/promotions you want for your boss to sign. This way you've got documentation for the court if your boss signs it and tries to back out because "they were drunk."