My CPAT was intense.
Best thing IMO is weighted stadium runs. Find the biggest football staidum you can get into. Strap weight on your back and get up there as fast as you can. This is hard on your knees so plan for that
Also get a sand bag from home depot or whever and work with that.
Me and another fighter help guys train for it using sand bags
Throw the bag, which is usally 50 pounds, if you need heavier, go to a army-navy store and buy an old ruck sack and throw sand in it, seal it up and your good to go, throw it over your shoulder, and run down field.
We work throw the sand bag over head, using a clean and jerk method to work big time on grip and full body power.
Just go out and run too. Make sure you have muscular and cardio vascular endurance and the only way to build that up is to run, run and run.
If your in good shape and healthy you should be fine. its not terribly hard, you just gotta be ready for it, but it sure is a blast, gotta love the stuff.
Also is it a local volunteer? Are you going to a Academy afterwards?