Leather stamping and working. It pounded the psych med induced doldrums and compulsion out of my mind on the top floor.
poo
Weaving - specifically, Tablet Weaving .
My friend has one of the better pages on the technique. With kitty pics.
Basket weaving. Seriously. I love it, and you can even make money off it if you get good enough.
There are a ton of resources online, and a lot of the materials can be harvested naturally (No idea where you live, but where I live I’ve got cattails and sagebrush alone to go on). I love basket weaving.
Another thing I love is sewing with a machine. I’m eternally clutzy and I have yet to have seriously injured myself, outside of stabbing myself with a pair of scissors from being stupid. I’ve sewn baby blankets, renaissance costumes, Jedi and Sith garb, Harry Potter robes, anime and video game cosplay, and original clothing. All from my own design. You can do that or you can learn with patterns (I’m horrible with patterns, they just confuse me, but apparently they’re really good for most people). Machines can run pricey but you can usually get a simple one new for under $70 at Wal-Mart. As I said, I have no idea where you live, but if you’re nearby I have a Brother (brand of machine, FYI) you could have - it’s minus a cord, though.
~Tasha
Beading. You could do needleweaving, or thread beads onto wire, or learn lampworking and make beads. If you are a single guy, you can;t go wrong with the “girly” stuff- knitting, spinning, weaving, beading, crochet have lots of social gatherings, groups, classes and workshops, 90% female, all age groups. So you can practice a solitary hobby, or join a community. Lampworkers seem to get a little riled up on the Friday night workshops,
Grab a couple of squares of paper, learn how to make a single unit and you’ll be able to do it without looking (at least I could 
though I’m kinda wierd.) You’ll have to make a lot of them to be able to make some of the nicer pieces, but it’s a great time waster.
It’s not exactly a handicraft, but I’d suggest: learn how to play chess.
If you have a laptop, you can get really good software for free or cheap.
You can get a really cheap set, and get books from the library. Sometimes, I get into studying or playing, and next thing I know it’s three hours later, it’s dark, and I’m hungry.
You could always subscribe to an internet forum, and start a thre…nevermind.
I’ve seen several things already mentioned that have worked for me: jigsaw puzzles, chess, and where others have mentioned weaving and knitting, mine would be macrame’. In each of these activities I have learned that I can focus on music (instrumental mostly) and block out pretty much all thought that’s not involved with doing the activity I’m focusing on. Hours go by and the world collapses into the activity.
Once I start trying to do things like crosswords and other word puzzles, or reading posts here at SDMB, and certainly while trying to type posts of my own, I have to turn off any distracting inputs like TV or talk radio so that my attention isn’t being divided. But with macrame’ and jigsaw puzzles, and to a lesser degree chess, whatever part of my brain that’s being used for those activities is unaffected by distractions.
You could get some Petoskey Stones and polish them either with polishing tools, or, apparently, your hands. I’ve been told by a Traverse City-ite (where the stones are most plentiful) you can actually get them polished by constantly rubbing them with your fingers and palms.
Macrame. It’s like untangling cable in reverse.
Embroidery, cross-stitching, sewing. Go to a crafts store and look around and see what you like.
I would second this suggestion - it totally takes my mind off of whatever’s bothering me, and is easy to get started in. Plus, after I got pretty good at it, I was able to make gifts that my friends drool over. I’ve even sold some stuff!
Weaving on a lap loom or knitting on a spindle or cross stitch are repetitious enough to calm my anxiety but interesting enough to hold my interest. Darning is also soothing. And people are always very impressed with my industriousness. I generally don’t tell them it’s really just to stave off that “We’ll never maaaake it, we’re dooooomed” feeling.
However, when I am really nervous or upset baking is certainly the gold standard. When I am extremely upset I make croissants. Dearly beloved periodically threatens to really set me off kilter just so he can have fresh croissants for breakfast.
I’ll add a second recommendation to try out Origami, it’s interesting, you end up with cool things to give to random people, and it has a very low cost of entry 
“Paint By Number” is making a comeback. You can even convert photos or other images to Paintings.
This might lead to more “serious” art. Or you could stay non-serious & just have fun.
Grip strength training.
As an underpinning to any other hobby requiring manual dexterity of the hands, training your hand grip can be very rewarding. There are some great ideas in this thread for “handicraft”, and strong hands are a foundation to a lot of them. What a lot of people, particularly muscular guys, don’t realize is that while hand and forearm strength are closely related, neither guarantees a strong grip or dextrous fingers. You don’t need to be a weight trainer to get into it, as hand strength can be casually developed in your spare time. The results are very progressive and easy to notice, and it’s something I’ve always been into. Perhaps before long, you’ll find yourself tearing a pack of playing cards in half if you really get into it. 
Google “grip training”.
Hey, that’s a good idea!
But it’s mental activity, wouldn’t it add more to my stress? 
I enjoy making necklaces out of hemp and beads. Plus, you can sell them to college kids really easily…
Brendon
I will second knitting.
It is a cheap start up. Portable. You can make it as difficult as you want ( sweater) or as brainless as you want ( just knit all the rows until you have a scarf.)
All knitting is is making a loop with another loop. It’s all loops. There are only two stitches: knit and purl. That’s it. You can knit in a car. You can knit on a train. You can knit while drunk, even in Spain!
It is a great way to make presents for someone and everyone loves to get a scarf You don’t have to knit for yourself; you can knit for charity which is how I got started.
Knitting Help free online tutorials.
Basic Knitting in print with illustrations
Knitty a fantastic online free pattern resource and their boards for every level of knitting. Two thumbs up for Knitty!
The best part of knitting: yarn…no, knitting books…no…using my addi’s…no…looking for the Ultimate Knitting Bag…No, it’s the social aspect and connectivity to the history of it all…hell…I like all aspects of it.