One thing that helps me is a checklist before I go:
CHANGE!! (yes, I've forgotten it in the past - LOL) PRICE LIST, GROCERY BAGS for purchases, BUSINESS CARDS, SCISSORS, STAPLER, PEN, NOTEPAD, WATER, SIGN IN SHEET FOR EMAIL ADDRESSES, CREDIT CARD PROCESSOR IF YOU HAVE IT.
As for the candles themselves, I'm still trying to figure out what works, but in the past I think we've tried to display too many scents. No matter how many you take, SOMEONE will ask if you have XYZ and of course you didn't bring it! I read somewhere that people get overwhelmed with too many choices and end up not buying anything. (And that goes for anything - not just candles.) So at our next farmers market, I'm going to narrow it down to maybe 6 scents, just covering the basics - fruity, floral, perfumey, etc. You can always give out a list of all your scents. For advertising, I like to give away a votive to anyone who walks by.
Hope this helps and good luck at the fair!! I'm looking forward to reading others' tips!!