That is an excellent idea. Now and then a person gets over-run with pots of all sizes and sometimes they get thrown away. I've been guilty of that myself.

I know I have some trays that I would be happy to put out at the swap for whomever might make use of them. Carmellia

Another good item is old mini-blinds. They can be cut into 6-8 inch pieces and make great plant markers. No need to cut them.. whoever picks them at the swap can cut to whatever size they want.

I don't need this one at the moment, but at times I would have been glad to trade for a pile of newspaper. There never seems to be enough on hand when building a lasagne bed.

Back issues of gardening magazines, or gardening books you no longer have a use for.

Name tags, markers, small tablets, pens (for identifying ourselves, and for making notes).

Food for lunch.

And, if you can't think of anything that you think others might find desireable... come empty handed! If you feel guilty, sit out the first round or two of the swap then join in. There are ALWAYS extra plants that people end up taking home just because they're extra and they can't stand to see a nice plant go to waste!