Aside from the advice already given, I would add that your backup gear doesn't need to cost a fortune. Sure, you can buy a second unit of your favorite amp if money and loading in/out is no object, but you can also save yourself a bunch of money and work by throwing a POD/micro head/whatever in your bag. Don't rule out a small combo amp as a backup either- they're fine at a mic'ed gig. Likely won't sound as good, but it will get you through, and as long as it doesn't sound like a swarm of bees raping your ears people generally don't care.
Another bit- simplicity is good. Fewer parts generally means a faster setup/teardown, and fewer things to go wrong. Taking a long time to get on/off stage is a surefire way of pissing everyone else off.
And keep some extra picks within reach.