Bike& run: easy riding til my core temperature is warmed up
Swim: front crawl at a slow pace until my heart rate is up
Gym: rowing machine for 2000metres
.
Crack my knuckles.
Seriously, I can’t swim if I don’t crack my knuckles in my toes before jumping into the water or putting on my shoes.
Other than that, the workout usually incorporates some form of warmup.