Hi Hannah
The prints in your shop look quite small so you have lots of possibilities.
Take a stack of paper coffee cups, put them upside down on your table and lean the prints against them. If they are not stable enough you could use them right side up with some sand in the bottom
Take an empty frame - no glass, no backing board - wrap string around it then peg your prints to the string as you have in your photos. You could use a frame made from stretcher bars in the same way. Use Blu tak on the bottom of the frame to keep it fixed to the table if necessary.
http://akinostudio.com/images/42.jpgMake tepee stands out of sticks - tie the sticks at the top and then spread the other end to make a stand - and lean the prints against these.
http://static.ddmcdn.com/gif/camping-activities-for-kids-3.jpgAttach the prints to blank canvases - use wide ones that will stand freely. You can use small magnets on the back and front of the canvas to keep the prints in place.
http://akinostudio.com/images/41.jpgPin some prints to the table edge.
My experience at this type of event is that people like to see artwork in frames so take one or two framed prints if you can, to help them see the possibilities.
Good luck with the show.
AM