Grounding techniques.
It puts you in the moment and promotes mindfulness. It involves observing your surroundings and all sensory input available to you.
Stop whatever you're doing. Breathe evenly. Look around you. Observe the color and size of the trees, the color or texture of the paint on the walls. Count the ceiling tiles. What do your feet feel like in your shoes? Rub your hands on your thighs, and appreciate the texture of your pants on your fingers and thighs as well as the sound it creates. Observe any smells or tastes available to you (some people carry small candies for this).
Whatever works best for you. The tactile/touching stuff works best for me.
They say that depression lives in the past, and anxiety in the future, so grounding yourself in the present is best. For me, it acts as an interruption/distraction.
I start doing this as soon as I start to feel that tightness in my chest that signals an oncoming panic attack. I am medicated as well, but grounding techniques have been a real game-changer.