I had a great weekly gig for quite a few years. We played the early set - around 6.00pm to 10.00pm before it got too rowdy. There was always a decent crowd, I got free drinks and we had a good sound system and a regular mixer. I limited myself to a pint per set (we played three sets) and always washed my hands before each set. I ALWAYS got nerves, usually starting as I woke up that morning. But the frequent gigs really helped, and back then my chops were pretty good from all the practise. Usually the nerves would disappear as soon as we started playing and it became one of the most fun things I have ever done.
Things I can concur on - NOBODY notices clams. And you will make mistakes. Don't grimace, don't apologise or freeze or anything. Maybe smile at a band member. The number of gigs where I thought I sucked and somebody would tell me it was the best gig they'd seen me play made me a little paranoid!
I kept a small towel onstage to wipe away sweat on hot nights. I hate having sweaty hands and trying to play. I used one guitar, one amp, a tuner, an overdrive and a delay. I had spare strings, leads, picks, tubes and power leads. Of course if you take spares you will never need them.
The main thing for me is to know the tunes well enough that muscle memory can take over. That doesn't mean you don't mean it, but it does help if your mind wanders... It's a bit like driving. I find that writing down the order of the parts in a song helps me remember it better too. I would write out "Intro/verse/chorus/verse/chorus /middle 8.." etc for each song. I didn't take that piece of paper anywhere - just the act of writing it out helped me remember.