The trick that saved me was making the routine portable, not location-based. 'Gym at 7' becomes 'move my body for 30 minutes wherever I am'. When the habit isn't tied to a specific place, a new city can't break it.
Every new city resets my habits — the gym, the sleep, the cooking, all gone for the first two weeks while I figure out where things are. By the time I've got a rhythm, I'm moving again. How do you carry a routine with you instead of rebuilding it from scratch every single time?