One of my favorite non-postcard etegami projects is hand-painted etegami drink coasters. You can slip one into an envelope and mail it as an alternative to the traditional holiday greeting card. Or let your party guests take home the coaster that was part of their place setting, as a souvenir of the event. A set of coasters makes a nice stocking stuffer or hostess gift. You can probably think of waaay more uses for them.
I like to leave my coasters un-coated so I can enjoy the texture of the washi paper. The sumi ink and gansai colors I use won't smear even if the coasters get wet, and they soon dry out anyway. They will, however, stain a bit from dark-colored spills, so when I give them as gifts, I often cover them with clear adhesive film to help them stay pretty longer.
Custom etegami coasters are now listed on my Etsy shop, if you'd like to take a peek.
Etegami (e= "picture"; tegami= "letter/message") are simple drawings accompanied by a few apt words. They are usually done on postcards so that they can be easily mailed off to one's friends. Though etegami has few hard-and-fast rules, traditional tools and materials include writing brushes, sumi ink, blocks of water-soluble, mineral-based pigments called gansai, and washi postcards that have varying degrees of "bleed." They often depict some ordinary item from everyday life, especially items that bring a particular season to mind.