Considering that he'll only have 10 days leave between Boot Camp and Advanced Training, you may want to make sure to buy him something he can take back with him.
He'll be required to live in the Barracks, he will almost certainly not be allowed to keep a fixed blade on him, or in the barracks. Discovery during a Health and Welfare Inspection could lead to loss of what little rank he might have, and a black mark on his "Page 11" that might well follow him for a VERY long time.
The only legal way to keep a "weapon" would be to sign it into the Armory and leave it there. He'd only be allowed to withdraw it after filling out a Hand Receipt for it, and could NEVER be allowed to have it in his room in the barracks. Advance Training will not offer this service with a smile, and may refuse to do it altogether, but his Permanent Duty Assignment is required to do so if he requests. (Firearms, archery equipment, ANY "weapon" will be handled the same way.)
I'd suggest a nice (but not TOO nice!) production folder of some sort. Something with a fairly short blade and not too offensive. I don't remember the exact length requirements, but you could always call up your local Recruiter and explain what you want to do, and ask him what is within regulation.
I won't go into how stupid it seems that you can spend all day shooting an M2HB .50 machinegun, and then go back to the barracks and get busted for having a knife in your posession, but it happens.
It's tragic, but even the Corps has fallen to the point where they are nervous about letting Marines play with sharp pointy things without supervision. (Of course, they don't really trust the Supervisors either.)
Check with the Recruiters tomorrow, and then come back, tell us what they said, and maybe someone can offer you the perfect gift idea that WON'T get your boy in trouble.
Semper Gumby.
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Desenfundeme no sin la razón, envaineme no sin honor
Usual Suspect
MOLON LABE!