I usually try to squeak out a pre-show poo and the rest seems to fall in place.
Mmm...yeah, I once clogged a toilet at a venue taking this approach!
My current band has no rituals, and I've let mine slip. I always tried to have a short jog in the early evening, and for a long time, I listened to either Live at Leeds or Air's Moon Safari on the way to the venue. Had to be one of those. Then my band would split a double of Southern Comfort before going on.
I think my current band needs something, like maybe splitting a double (or more) of Jack. We have adopted a musical ritual though -- as soon as anyone yells "Freebird," as someone inevitably does, we're playing it. We're an original band that plays nothing like Synyrd, so it catches them off guard.