One great ref I was with regularly a couple of seasons ago had some good warm ups when we had enough time.
One is a simple ref in the middle jogging forwards and backwards, ARs crabbing either side following, then ref turns and sprints and ARs chase.
The other was more of a brain and body sharpener. Take turns in a corner, someone is x-axis e.g. sideline, another is y-axis goal line, x and y move slowly at first not so far up and down the lines... your job is to keep moving with them staying at their intersection. You can make it harder by facing the corner, even harder by facing away from the corner at 45 degrees, and getting quicker.
Got any more of these?