What are some good gifts to bring to Europe from San Francisco?

Something edible is often best - you will not know their decor other than the picture or two on the AirBnB website, but food that represents SF would probably go over very well. What about some Ghirardelli Chocolates? I bet they even have some sort of SF giftbox. Go to http://ghirardelli.com/

Some California cuisine is always appreciated - local jams/jellies or canned goods travel well, and California is known for its abundant agriculture. Local wines are also a good idea & there are many wineries in the greater Northern California area. I'd also suggest looking into chocolates. Both Ghirardelli & See's are well-representative of the area. For non-food items, good photos of iconic places usually resonate well with people. Many photographers have great photos of the Golden Gate Bridge, etc. You can also get inexpensive art prints as cards, allowing you to write a thank you & indicate your city of origin tastefully. A mix CD would be cute - either of SF-based artists or songs that reference your hometown. Overall, those ideas are all under $20 (most well-under), and a couple of them together would still run you less than a twenty and be a thoughtful expression of gratitude. Happy traveling!

The magnet version of this poster http://www.streetcar.org/store/travel.html#celestial-nights.   Inexpensive, small and representing something unique to San Francisoc.

In Europe, SF is characterized by: the Golden Gate bridge, the little Victorian houses, the up/down streets, and the cable cars. Small models of the cable cars or any depiction of the above, will be a hit.