I wouldn't put in plastic bags, and I also wouldn't cut the fabric. I would measure and pin the length to each fabric so the buyer knows how much is there.
Would you be able to cut at the sale? If so, you could have a sign that you will cut longer pieces to 1/2 yard or 1 yard increments on request. The cutting at the table slows everything down, plus it is easiest if all yardage is priced the same per yard, so you might want to skip that. I wouldn't put fabric in plastic bags because quilters like to "pet" fabric.
Think about how to organize the table. Perhaps longer pieces folded and stacked, with yardages pinned so people can read the yardage for each piece without taking apart the entire stack. If you have lots of this kind of fabric, perhaps color code each stack, or organize batiks in one stack, civil war in another.