The tickets seem to be more then enough for a great Christmas gift! You could get him something like a CD to go with it or go all out and buy a jersey to go with the tickets for him to wear to the game. That would be a great combination of gifts.
That is a really nice gift. You can buy him a nice t-shirt or a perfume. You can also buy him some nice accessories because they are always good items that you can buy for him. Watches are very popular among young boys.