I have done a lot of craft fairs, but mostly with my pottery, which is my main source of income. I can give you some tips as far as general booth display goes. Try and avoid the "everything thrown out flat on the table" look. People like to see different levels, it makes the booth seem more exciting. You can just use boxes under fabric to create a variety of heights and maybe have some old vintage suitcases, or nice glass bowls that you put buttons in (or whatever). Also try and make some groupings of product. You could display a bunch of water bottles with your labels on them to create a colourful group and show people what they look like in use. Don't forget to drink out of one and wear your buttons during the show! You will generate interest that way.
Something that has worked for me for button display is a jewellery hanger like this:
http://www.makeit-loveit.com/2011/08/hanging-jewelry-holder-space-saver.html/space-saver-jewelry-hol...Then people can see a lot of the button designs you have, rather than pawing through a bowl to find the different designs (although that can be fun too, I do a bit of both). You can fit 4 or 5 buttons in each pouch.
Here's another post in this team dealing with craft fairs:
http://www.etsy.com/teams/9498/pinback-button-lovers-of-etsy/discuss/9057372/Also remember all the non-display stuff you'll need like somewhere to put all the cash you'll make (YAY!), a float to make change, etc. Don't forget to create a space in your display where you do your transactions.
Good luck and have fun! :)
Forgot to say, lighting is important! Some places don't have enough lights, so if you think it could be dim then definitely bring some lights, it makes the buttons sparkle. There is nothing worse than putting a lot of effort into a booth and then having it look dull because the lighting is bad. Those long "arm" clip lights are good.
