I'm assuming by favors you mean the little gifts you give all the guests? I'm not finding anything that is traditionally considered a party favor that is knitted.. Hmm....
Bride and groom finger puppets maybe? A cute endangered animal one that maybe the couple support? Here's a basic finger puppet pattern or two..
Bookmarks that have hearts or are embroidered with the couples names and date of wedding? (use lace weight so they are thin!)