Ask HN: Stay productive while commuting offline

I live in a city where I have to spend 30-45 minutes in subway commuting to work. And subway is really a train moving in tunnel deep under the ground. Unfortunately there is no internet connection there and it's boring as hell. From another side, it's not me who's driving, I have both my hands free and can focus on reading safely. I cannot pull out laptop and work, not that much space around in peak hours. Phone is totally available. maybe tablet. I cannot read HN, because it's obviously a website with links to other websites. What are my options to stay productive?