I have a few craft shows coming up this winter. I order from Uline.com or Paperline.com
You can pick paper or plastic and different sizes and buy in bulk so it's cheaper and you'll have them for shows to come.
I think I got 1000 7x12 bags for like $23.
ooo if you get paper, you can tell the buyers they can reuse for the holidays!
Tablecloth...Depending on the space/table size, in the past I've used a small bed sheet if you've got one or you can always get one at the dollar store :)
[If you buy at the dollar store, get 2 and some tape as their sizes are usually smaller]
:)