You're going to be manically busy - so here are the things you might not remember to do...
Don't forget: to have a good night's sleep...
...Because you're going to be busy.
Don't forget: breakfast
Nobody wants to hear a rumbling stomach echoing through the ceremony venue as the bride and groom say their vows. Even if you're not much of a breakfast person, force yourself to eat - if nothing else, it will line your stomach for later!
Don't forget: to pop the bride's waterproof make-up in your bag
As well as any other extras she'll need on the day. Think tissues, chewing gum, a snack... Oh, and your phone charger.
Don't forget: plasters
Your feet will thank you. Seriously.
Don't forget: have money on you for the bar
You might well have drinks bought for you all night, but make sure you have some cash on you just in case.
Don't forget: to keep on-top of any tasks the brides has set you
From gathering people for the photos to liaising with the DJ about the first dance: remember everything the bride and groom have asked you to do.
Don't forget: you will get a mention in the speeches
Traditionally this will be from the groom, and perhaps the Best Man, too. During the speeches, you'll laugh, you might cry - and you'll almost certainly receive a gift.
Don't forget: to book a cab to take you home
If you're not staying overnight at the venue, order a taxi in advance to take you home - make it cheaper for yourself by sharing it with others who live nearby.