I also usually include one or two promos in my online sales shipping packages. I especially like the cards that have coupons on them.
My promos for the swap were mini ribbon bookmarks. I also included business cards with coupons on the back. I just recently ordered some "I Heart Handmade" personalized pins from http://sassycat.etsy.com/. I just love them! They are so cute and colorful. Hopefully, my customers will pin them to their bags and remember to order from me again and again.