carry a book or project with me to work on during periods of free time of indefinite length

I’ve been writing a novel since I was about 18 (8 years ago). I started it in the 3 month summer holidays at uni, but drop it as soon as I get busy. Now that I’m in the work force I don’t get as many quiet periods, but I still find the time, like when I’m on a long flight.

I need something to pick up when I’m waiting or there’s a break that I can put down again at a moment’s notice, especially now that there’s a lot of down time at work that isn’t long enough to really do anything or in which I’ll be called on to start again but don’t know just when.

Kids books have worked well in the past, or short texts—perhaps some poetry. I’d like to have something like a simple knitting project, or vocabulary cards for a foreign language. Perhaps I could work on memorizing a poem.