Hello, Tamara! My general policy has always been a 3 packet minimum; however, if the average number of packets falls below a certain number per person, I reserve the right to either call for members to add more packets or to cancel the swap. We always have a very generous group of participants, though, so it never seems to be an issue. I always say to contribute as much as you feel comfortable contributing.
Usually, established gardeners have dozens or even hundreds of seed packets to contribute, but the minimum is set low to allow new gardeners the chance to join the swap and collect seeds to help them get their gardening start....and then they can return the next year with a greater number of seeds!
I haven't listed the details/rules for this Fall's swap just yet, but they should be nearly identical to the previous swaps. You can view the details from last fall's swap here:
https://garden.org/apps/swap/v...
I hope that helps! If you have any other questions, please feel free to ask them in the FAQ thread (within this swap).