We do 2 sets of 13 songs, which seems to be plenty, though we are expanding it all the time.
Now, I'm not a gigging expert or anything, having only played 3, but I will say definitely take a spare guitar - even if its a bit cr@p, its very handy to have - if you break a string, its very annoying to have to change it quickly under pressure.
As for the PA, in my band, we have a Behringer mixer of some kind. People always seem to slag off Behringer, but theres nothing wrong with it, and has been used by the drummer for discos every week since he got it, with no problems. Not sure what speakers we have, big JBL ones of some kind I think! Monitors are another thing, we have 2 old Carlsbro monitors which seem to work well. Oh, and take a spare of every cable!
As for the mic, 1 SM57 would be sufficient for guitar I would've thought, and SM58 seems to be the standard for vocals.