Not trying to be a contrarian (it just happens!) but boredom will not kill you. In fact, I challenge you to sit and be bored for a good few minutes. It's good for you. I'm terrible at it myself, but that's what being a dopamine crack addict will do, I guess.
If you're out of ideas for things to do, try mindfulness meditation (Waking Up is an app with a bunch of free lessons to get you started) - very little woowoo, just pay cursory attention to something, then when your mind inevitably wanders off, just "notice" and be, well, mindful. It's like an antidote for boredom, in a weird way, and studies have shown that for whatever reason, it's good for you.
Myself, I read books for any "random short term downtime".