On Ravelry, I'm usually in the monthly card swap on the Tiny Owl Knits group. It's one card and if you want to add something as long as it still fits in a flat envelope that's a choice. (they had some issues with bubble envelopes not getting to their destinations - especially overseas, and trying to keep costs down.) But for the holidaze, I did that swap, The Cave (group for hermit and recluse wanna bees on Ravelry) had a card swap (just a card) everyone sends to everyone, if someone didn't want to mail overseas they would just get domestic partners, and if you wanted to do it by email, only partners ok with email. So I think that was 26 cards.
And then I thought the Card Swap concept was such fun - that I ran one on Backstage Team Fraggle (the group for the Nerdwars/Nerdopolis Fraggle teams).
Then at the last minute Team Iron Throne (another Nerdopolis team) decided to do one - only it was three partners and each partner had a secret word that you had to put in their card. When you received your cards - your code words spelled a phrase from Iron Throne.
My phrase was "Words are Wind"
I have a thought... I'm going to use christmas cookie cutters and cut out the images on the card. Use crochet thread to crochet (hopefully - never crocheted with thread before) a "frame" then use Christmas coloured fingering weight yarn to attach them all into a garland for next year.... eventually I WILL have a handmade tree! (well not tree but decorated tree)