Oh come on, it takes an hour, tops, to make salsa. Then what is he to do with the other 9 days and 23 hours? 
Without knowing where your specific interests lie, I don’t feel qualified to make a useful suggestion. In my spare time I brew beer, write songs, play ukulele, and study Spanish and Mandarin. Those things are all very enjoyable, if you’re me, but no way would I spend 8 hours a day for 10 days doing any of those things.
Learn how to can, I spend a lot of time smoking and canning salmon, I also make and can jam, bull kelp salsa and relish, and sea asparagus pickles. Its fun and months later you are stilll enjoying your work
The dance!!!
Buy a used unicycle and learn how to ride it. If you master that, learn to juggle while riding it.
Origami, fun to do, challenging to learn, always amusing to children, all you really need is some magazines with shiny paper, to get started. I learned from a Korean girl when we were trapped on our bungalow porches for a couple of days, during torrential rains, in Bali. It passed the time, was fun, and I’ve since amazed many children with my talent. Give it a try.
My other suggestion is find a neighbourhood kid and help them build a fort. Mind you, you have to let them do the designing. You can make suggestions, but they have to approve. Your participation would be awesome for them.
You nailed it, but I’m grateful to have the time off. Lots of good suggestions so far. I’m definetly going to take the magic and origami suggestions. The beer one seems interesting too.
In the past I’ve tried to teach myself programming but finding a cheap or free system to learn on has proved difficult. (well that and learning arrays for some reason)
Thanks again, I can feel my horizons broadening already.
I like the origami idea, but this one might not go over so well.
Adult: Hey kid, want to come into the woods with me? I’ll help you build a fort!
Kid: Um, I better ask my dad if it’s OK…
Take up knitting or crocheting. Don’t buy those “Learn to Knit/Crochet” kits, though, they have crappy yarn and hooks/needles. The crappy yarn is nearly impossible to work with, and the needles/hooks tend to bend or break, and are similarly impossible to work with. Despite my distaste for Hobby Lobby, they have a decent house yarn called “I <3 This Yarn” in acrylic, which is fairly cheap. I’m not as fond of their cotton yarn, and I’m allergic to wool.
There are a number of online videos which show how to start the project and work the various stitches, both on YouTube and on craft websites. There are also any number of websites dedicated to the crafts which have still pictures.
I taught myself to knit, crochet, tat, and embroider from books. Some books are not well illustrated, but most books have decent instructions and pictures.
I’ll resubmit my suggestion from a previous similar thread: knife throwing. All you need are a set of throwing knives and a block of wood.
Knitting!
Portable. Affordable. You can make something for yourself. You can make a gift. You can make something for someone in need.
Yarn is like crack.
Only legal.