During a regular work day I'll be at my home-office hacking away some code, doing accounting, skype-attending meetings or other things I can do at the comfort of my working environment... when I have to step out of my office however I can't always carry my work station with me or more like I don't want to. Some of you like bringing around laptops or even tablet devices however I don't like carrying this stuff with me, plugging them, making sure they don't get stolen etc. It's too much work. Instead, I will have my smartphone, a pair of small earphones, a notebook (not a laptop an actual notebook...) and a pen with me at all times and will make use of these.
If a design element needs to be thought out I do this with the notebook and the pen. If there's no work I can do I make sure to follow up on the GDC talks or other youtube material I haven't followed. In some other cases I will go through my multi-reddit and read news and threads related to game development. Sometimes I will go through twitter and see what other devs have been up to. You can do all these things with the help of your smart phone nowadays. You need to keep yourself up to date with the discussions and materials that have been circulating especially since the industry is updating hella fast nowadays.
This habit is especially good because it will force you to take a step away from 'actual' development and will divert your attention to the industry which you are developing for!
In Sid Meier's Pirates wind was important business.
A lot of youngsters don't realize how important it is to be aware of now. You have to think of it like smelling the air and watching the horizon. If you don't do these things you won't be able to catch the wind that will take you to land or spot the storm that will crush your sails.