My mother-in-law recently celebrated her birthday. Getting her together with her three sons and their families was challenging based on different schedules, but we were able to get everyone together for afternoon desserts. Each family brought a different dessert (Williamsburg Bread, Orange Cookies, and Apple Pies), and we spent the afternoon watching the grandkids, chatting, and feasting on desserts (...oh, and her men may have talked her into watching the Skins game as well).
Decorations came from the season... pumpkins, gourds, indian corn, acorns, and corn husk flowers. Autumn colors dominated with browns, oranges, and golds complimented by the cobalt blue. For flowers I mixed two grocery store bunches - one of eucalyptus and greens and one of yellow and orange flowers - to create custom arrangements for the party.
This is such a simple option for a quick gathering. Almost all the decorations can be picked up from a farmers market or grocery store, and it takes no time to assemble. Just grab some pumpkins and have fun with it.