For me, getting/staying undepressed is a function of doing something that's (preferably) creative, and interesting to me, and promises to be somehow useful.

Personal note: what I do for a living* is typically all three of those. When work runs short or I get rained in or something, I may fall back on inventing some gadget that will (maybe someday) make a job easier or writing a few computer programs to investigate something of interest to me. I've been known to find myself a bit depressed (and to go back to bed for an hour or two) if, say, I've gone to do a job for a customer but they've no-showed. That lasts only about as long as it takes me to find something else I want to do with the time.

(I do have a wry standing joke that when there's some interesting project I want to do, and I'm working steadily and have the money to do it, it's hard to find the time; but when work is slow and I have lots of time, I'm watching the money and seldom want to invest in an expensive project.)

^ Actually, the above information is a bit dated because more recently, my favorite creative activity has been reading/posting/participating in online communities such as PC.

(justme, how does any of the above work for you?)

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*Oldish cartoon. Woman with surprised expression, to man: "A professional nerd?! Can you make a living at that?"