Yes.
How the MAG swaps work (which is not the same as all swaps I've been to) is that

1. people post "have" and "want" lists before the swap and set up prearranged swaps - which aren't necessarily one for one swaps. For example, if I have 25 ditch lilies to get rid of, I'll be happy to give you a couple, whether you have anything to trade or not.

2. People bring plants (or pots or magazines or garden tools) to the swap and trade (or give away) on site.

It's not that common at MAG swaps for someone to be only willing to swap what they think is a highly desirable plant for something they think is desirable and rare. Generally people use these swaps to give away the extra 10 tomato plants or annuals they couldn't resist starting, and take home something they'd never heard of. Some swappers are aficionados of various plants that are rare and desirable to the rest of us, and they are happy to swap them for just about anything.

Can I just show up with pots and flats of extra plants that I have? It doesn't have to be something that's been specifically requested or pre-arranged correct? What about flats of seedlings or are mature plants preferred? How about extra seeds? Sorry for all the questions.
Karyn

Yes, you can just show up with stuff (that's what I meant by #2, maybe it wasn't clear). Seedlings or mature plants, or seeds - all good.

After the prearranged trades are arranged, MAG swaps have not depended on one-to-one me-and-you swapping (not that all of the prearranged are one for one or only direct trades by any means). We sort of figure that all the swaps even out in the end. So if you don't have anything I want, I give you some of what I have that you want, some body else does the same with me.

In the past, we have also said new gardeners just bring brownies or other great food and take home people's spare plants. Last year, there were some problems with plantless people arriving early, swooping down on many plants including many a prearranged plants (especually irksome sometimes ignoring the "if it has a name on the label or bag, it is spoken for").

While I am not proposing a traffic cop be appointed, I do suggest our plantless new people start their taking a little later in the morning. Perhaps keeping in mind our after lunch rule: If you touch a plant you have to take it and if you ask a question about it, you have to take two. And if you leave your car unlocked you may find some one had put Autumn Joy sedum plants in it.

You'll can start yelling at me now for being a meanie.

KimKa

P.S. Bring just about anything garden related, seedlings, divisions, plants, trees, pots, buckets, magazines, tools. Just take home what ever doesn't find a home and make sure it isn't some one's stuff before you make off with it.

I came to my first swap last year with a few flats of seedlings, four or five bags of horse manure, a shade cloth, bamboo stakes, a ball of twine, some packets of seeds, a plastic tub, a pH tester and a few other garden oddments I figured I wasn't using. I was surprised at how many people wanted things I thought were garden leftovers and delighted at how generous the other gardeners were.

I was also surprised (and delighted) that the general MO was not "swapping", but the stuffing of plants into other people's hands. Many people come expecting primarily to give plants away.

If you are browsing someone's plants, however, and if the plants are not marked "help yourself" or "free to a good home," do ask the owner if it's OK to take.