For me, it's physical exercise. And, concrete coding (as opposed to reading specs, designing, modeling or proving). It's easier for me to not do them than to do them, but I'm always amazed at how refreshing they are.
My strop is a strop, and I use it on my razor before shaving.
Coincidentally, the practice of straight razor shaving tends to put me in a state of relaxation and reflection that has a positive impact on the rest of my day.
For me, it's physical exercise. And, concrete coding (as opposed to reading specs, designing, modeling or proving). It's easier for me to not do them than to do them, but I'm always amazed at how refreshing they are.