I'm not always certain that relaxing and de-stressing are the same thing, so I will share what helps me to remain calm in uncertain situations.
Familiarity: Similar to Katie, a familiar element in any situation calms my brain. That element can be music that I know well enough to sing along with, or it may just be items nearby with which I'm familiar. For instance: I just moved to Birmingham, AL. I brought two suitcases with me, so none of the decorating elements in my home are familiar. I was using a vacuum that we'd borrowed from our leadership and noticed that it is the same model as the one used at my previous job. My housing is completely different, the people around me are completely different, but it's comforting to be able to operate this vacuum without any confusion or frustration. It's an element of mental ownership. Any time that I can control something in a situation, even if it's only myself and my brain, I stand a little stronger wherever I am. Some people bake and some people craft, some people just need something they can look at and know, "That's mine."