To add to this, try meditation too. It can be done while sitting and with the noise around you on a train, and you don't have to look odd by closing your eyes (

To add to this, try meditation too. It can be done while sitting and with the noise around you on a train, and you don't have to look odd by closing your eyes (though you could pretend you are sleeping). However I find it is most comfortable in a private place. I usually listen to music or try to read if it does not make me nauseous, but nothing to do with my studies.