Here is a list of my favorites:
Greek pens and pencils - forget the scenic ones designed for tourists. Find the local stationers' shop and buy cheap Bic pens with Greek lettering. They will remind you of Greece every time you use them.
While you're at the stationers, look around for Skag spiral-edged notepads. They're made in Greece of recycled and wood-free paper, and, again, their covers are printed in both Greek and English lettering. I've become so addicted to carrying one in my purse that on my next trip I'm purchasing them by the dozen.
Kitchenware from Greek housewares stores - If you're fortunate enough to pass a shop with pots, pans, and glassware in the window, pop in. I guarantee you'll find small, easy-to-pack, inexpensive items that will do a job at the same time they remind you of your most recent trip to Greece. One of my favorite items - the small glass pitchers often used to serve barrel wine at Greek eateries. Pick up a dish towel or two to wrap them in for the trip home... but be aware that some of the Greek-themed towels may have been made in China.
Clips -One handy item that you can actually find at most souvenir stands are the double-sided enamel spring clips. These are not inexpensive for what they are - recently, they've been going for about 5 Euro each at airport stands, 3-4 at souvenir shops - but they are handy and durable and just the thing to dress up a dull office wall pocket. These tend to be location-specific - Cretan designs will be mainly found on Crete, Athena's owl is most often seen in or around Athens, and so on. So this is one time when the next island (or airport) may not have the same thing for sale - grab them when you see one you like; remember they are all-metal and a bit heavy for their size, and they will show up on airport X-ray machines.
Toiletries - Lip balm lasts for a long time and every time you use it and see the Greek lettering, you'll think of Greece and the little island stand where you bought it.
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