I’ve been going to estate auctions or over 20 years and working them for a couple of years.  They range from terrible to great.  One of the main problems with auctions, is that the auctuioneer will want you to work all of their sales, and not let you pick and choose.  I have worked several where I lost money or just broke even, and there have been some really good ones.  The ones that seem to be the best are the country farm auctions.  Usually you are the only option for food and drink.  Sales in town are usually worse because there are fast food and convience stores nearby. 
 
I try to keep my prices reasonable, as auction people are usually looking for a deal.  The vendors that charge high prices (event pricing) usually don’t last.   Coffee is big during the cooler months, although I usually have a pot on at every sale (I work out of a trailer, so I have a little extra room over a dog cart).  I also have a pot of hot water and tea bags (not too popular but cheap), Spiced Cider, and  Cocoa packets at the cooler weathern sales.  Doughnuts do OK at sales that start early, and I find that if you individually bag the  leftovers and freeze them, they aren’t too bad (for my own use, not to sell).  We lso do breakfast burritos at the really big sales that start early.
 
Candy bars and chips do OK at some sales, especially ones that people bring their children to.
 
During hot weather bottled water sells like crazy.
 
Jeff
Black Hills of South Dakota