An enthusiastic cross-country skier told us that he always carries his skis around in his car so that he is always ready to ski whenever the moment presents itself. The same is usually true for serious photographers, who have a camera handy wherever they find themselves.
For a serious writer there is every reason to emulate this by carrying a small notebook and a decent pen at all times. I find that my lunch break at work is one of my best times for writing. It helps to have a limited amount of time. My motivation to write is very high.
You quite simply never know when a good idea will strike. I usually have a pad next to my bed and carry a journal in my brief case throughout the day. I’m rarely far from my journal.