There's a good size craft fair in JP, at the Unitarian Church right at the Monument, on the corner of Eliot and Centre Streets from 10-4 on Saturday. I will be there with my wares, and there's always lots of different kinds of crafters. The church also holds its annual book sale/yard sale/barbecue so there's lots to do. And if you've never been to JP, you can mill about the neighborhood and its funky shops, as well as the original JP Licks.
So come visit! It's supposed to be nice out, so it's a great day for walking around!