Take an open source git repo you've made, or open source a project you've got somewhere on your hard-drive and a) polish it (absolutely without adding new features), and b) document it. Both will teach you new skills and stretch you as a developer in ways that might surprise you. They'll also help make the ecosystem better for others, whether you have 2 or 2 thousand watchers.
I'll say stay away from devices as well, but I mainly mean staying away from social networks, news sites, and anything else that's idle browsing/talking. Also, stay away from work. Too much work, work, working all the time. Come up with new ideas, write blog style posts amount different subjects, look out the window and think, think about where your life is and where it could be, read some good books, etc.
Building a startup (actually others are doing the building, I'm doing everything else :) I would bring one or two books (Traction, Lean Startup, Smartcuts, etc.) and my iPad.<p>I would use some time reading and some time writing either ideas/notes or blog posts.
sleep.
try to stay away from devices, see if you can even do this.. :) - meditate
take a pen and paper, write down random ideas
plan your day/week
ignite a conversation with someone sitting next to you.
I tend to take time like this to simply write. Be it reflecting on the last 6 months of my life, or some sort of short fiction. Sometimes its good to forget about coding and look at the bigger picture.
Start a $10 billion business like this guy did on a bus trip:<p><a href="http://www.bbc.com/news/business-27579790" rel="nofollow">http://www.bbc.com/news/business-27579790</a>