As a serving soldier, he will be allowed anything legal to own to be in his possession.
What trade is he going in as? When I was in (1992 - 2005), the army issued jackknives to the worthy, but, like issued watches, getting one was the real trick.
Depending on your budget, what about a multi tool? A bit more utility and the ability to have his regimental number and name on it (this may also deter the chance of it going walkies if it’s easy to identify).
He will be allowed to use it in the field, very handy for cutting green string, tape and foliage.
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