On a serious note, go easy on the booze early doors.
People keep handing you glasses of this that and t'other - way earlier than you would normally consider it appropriate to start drinking. Unless you are already accustomed to beginning a hardcore 'session' at 2pm, take minimal sips - discreetly tip out warm stuff into planters/shrubbery etc, and top up with fresh if necessary. This is a wedding, norms do not apply, do not consider it wasteful, self preservation is all that matters.
A wedding is a marathon, not a sprint.
I once was a Best Man - as difficult to believe as that is - and before i gave the speech, nervous wreck that i was, i was given the most calming advice. It was given by a man that we shall call John, for that was, and indeed still is, his name. He said that the audience i was to face was essentially 'rooting' for me - nobody was going to be wishing me ill. To know that i was about to face an audience of well-wishers was a lovely thing - i ended up enjoying it more than many of the other things that i have also enjoyed doing.
Remember that.
Whatever happens, everyone wishes well of you.