Others have posted the main points, good suggestions all around. A few things I don't think have been mentioned:

Someone else said get snacks ready, I also recommend eating something substantive beforehand because you may lose your appetite, find it difficult to eat, or simply forget to eat later.

I also recommend taking care of any chores or "things to do" lingering around, so you avoid worrying about them at an inopportune moment.

To add to what Ennemi said, also it's a good idea to have a "trip sitter" or someone in the group who will be sober. Since you said you're doing it with experienced friends they probably know this already so this is more for your information. (I just saw in your reply that you are already on top of this. )