I typically (especially on the weekend, since at work I somehow have higher motivation to push myself) go down a "thinking cascade" to adapt to this, where I'd code for some time, then when my brain gets tired go do something involved but not too involved (like figure out how to do something with Linux or whatever, or read a book that is actually useful), then when I get tired of that go read medium-effort stuff, like history or check how to do some project around the house, then when my brain is completely fried I'd go comment on hacker news :)

Or eventually just go exercise and do chores... I find I can reset to the beginning of the cycle in an hour or so.