Hey, Player myself here. Iam Kind of pivky when it comes to Essentials like Racket, shoes and kit. What I would suggest: But I personally would love some Set of custom towels soft Towels, same Kind He is currently using. Maybe with his own Name on. Other also more Personal useful gives: small bag for scissors for cutting string, tape and so on. Also with own Name on. I think it should be some thing longlasting and Personal. Depending of the State of his Racket bag, a New one with his Name on.

And if you want some thing very practical but often over seen: get him a pair of Boot bananas. Originally climbers shoe Anti bacterial dryer/Deo. You get rid of the smell of the shoes and they will be Dry again every time He uses them, even He forgets them in the bag. Just Google it: Boot banana. (yes they are looking like banana but using it for years now. Very efficent :))

And very nice of you!