Simon recently found these envelopes with picturesque scenes of Tahiti, that he saved from the time he spent there during his military service. (That's a whole other story!) I love that they have the postcard picture, but can hold a multiple page letter rather than the usual small space on the backside of a postcard. Relics from a time before email and instant messaging.
So if you are on your next trip and looking for souvenirs for friends, maybe send a postcard instead!