My saga's favorite reckless magus is stuck in a faerie regio for several years of game time - it's a pleasant place but not particularly cutting-edge. He has no laboratory and no other people around. In terms of seasonal advancement, I know that he can Practice various Abilities. I couldn't really think of anything else he could do. What am I missing?
Craft magic should allow him to construct a crude lab with the available materials.
He can hunt supernatural residents and study the extracted vis. You do not need a lab for that
He can try to leave as well 
Xavi
Probably the best use of his time 
He could also negotiate with the locals for better things to do. Some of them -may- know some real abilities they could teach him, or may at least be able to presto up something resembling a lab. This might require some encouragement, but as a magus he should have a nice list of things to encourage them with.
With a little craft magic he could also put together the materials to do some writing.
He could invent a new mystery cult. The first Intiation, based on being stuck in a fairy regio for a several years, is well underway.
He could adventure if there is anything worth adventuring against in the regio. Or look for vis, possibly by hunting faerie creatures; and then study it, which does not require a lab. There might be side effects from studying faerie vis, though, and the botches should be interesting.
Thank you for the ideas everyone - please keep them coming!
Regarding craft magic to set up a lab: how difficult do people think that would be? (Assume that the magus is young with negligible Finesse.) How much time would it take?
Well, it'd certainly be at least a season to set up a lab, with potential for all sorts of nasty warping if he's sponting to do the craft magic work, which is likely. Also, unless he has a high finesse, chances are good they'll be not the best of tools. If you use Covenants, I'd look at some of the flaws, like poor stores, poor equipment, etc... he's going to be missing a lot of stuff. You might even decree that he must stop at having a basic lab.
Oh yeah!. Practice spells towards Mastery.
And he could practice Finesse as well. No need for a lab to do that and will improve his chances of setting up the lab later on.
Studying (Realm) lore should be easy if you are stuck in a regio. If it is magic lore, remember that if your total of Int + Magic lore + aura is 9+ you can enrich items. No lab required either. However, as per the RAW, a hermetic magis cannot use those items since he has a MR of 0 or more all the time.
Cheers,
Xavi