If you place the shirt in the ziploc, it acts like a buffer, think tissue paper. The shirt doesn't get as wrinkled like it would just being compressed with everything else. Basically it is a home made space storage bag like they sell on TV at 2 a.m.! Remember to remove all air from the ziploc bag.
Folding is also key! Fold the bottom up that will be tucked in anyway 1st, than fold again. Sleeves the same way, do not do the in/bend back over, instead in and bend down. I know that is hard to get. Just think folding the shirt in 1/3rds. You want the sleeves to lay flat on each side. this way they will not have creases in the arms If you fold in the shoulders too close the sleeves will need to be folded back to make it fit. If you bend it down at the shoulder, in an angle the sleeves will not have a crease. Shoulder boards will pop out the crease at the top of the shirt, meanwhile the arm is perfect. They get graded on uniforms.
After 20 yrs of Bullet being ADAF, ziploc bags are the must have to reduce wrinkles in clothing when traveling with this type of luggage.
The other tip is to take his pants and his tees, use the tees like you would tissue paper regarding folding. Place the folded tee mid thigh, fold the below knee portion up, than the top portion down. The tee will be less wrinkled and so will the pants.
The beauty of the blues is even if you don't do this they will eventually come back (G bless polyester!), but IMPO 10 minutes of repacking is worth it if it means less stress on them.
The one I would stress is make sure he has ziplocked his shaving cream, shampoo, soap, sunscreen, etc in baggies. The same is true if he takes Gold Bond powder.
Their luggage will be tossed around at the airport onto the plane, off the plane onto luggage claim,, than onto the shuttle to Maxwell, off the shuttle, to the Q's. If they are not secure and it breaks it can go on their uniforms, binders, folders, etc. causing frustration minute 1.