How much you willing to spend?
If he's a reader, any of the books may be good. I've read both Starship Troopers and had to read "The Art of War" as a cadet back in the day.
The good rugged watch is always a win if he wears a watch. The knife is almost always a good gift.
How Gung-Ho is the young man? Is he the type to go into one of the combat arms branches like Infantry, Artillery, Armor (sorry, is that Armour in Canada, LOL.) Or more of a support role such as Signal/Communications, Logistics, Medical, or any of the many supporting roles.
It really depends more upon his interests and your budget.
If one is worried about him enlisting and then getting trapped by one of the many enterprises that prey on young service men and women outside bases (we see that in the US, less than honest car dealerships signing up a newly minted soldier, or even young officer to buy a car for outrageous terms) maybe something that will help educate him on how to live modestly. Some Dave Ramsey books and/or The Millionaire Next Door.
Not saying he has to be a barracks rat, never going out and doing anything. But he doesn't need a $500+ / month car payment and insurance and then never has any money because it's all going to the bank and insurance co.
Not sure how things work in Canada, but suspect human nature is pretty much the same internationally and there are sellers who prey upon inexperienced young people with newly found money.
