Pick one upper-body exercise and one lower-body exercise that complement each other.
Pair an upper-body push exercise, such as an overhead press or a push-up, and pair it with a lower-body exercise that includes some form of upper-body pulling.
Usually, that pull in the lower-body exercise is isometrics.
Such as a deadlift, single-leg deadlift, or kettlebell swing.
If you feel “cold” or “old,” do a quick warm-up with a get-up or two on both sides.
Then, alternate the upper and lower body exercises with whatever time you have left.
Depending on the exercise, I like the reps somewhere between 2 and 8.
Rest enough between the sets to be able to talk somewhat ok.
Then go again.
This simple combo works well for a longer workout too.