For soldiers, I think a real doll is a very good choice. Use a photo of him to make his face shape, and then make a doll of you in military uniform, and then make a doll of you, just like the two of you will be together forever. Such a birthday gift will definitely be very special.
Since you finally meet each other once, and it is his birthday, of course you have to have a romantic birthday party. In fact, it is better if there are only two of you. Prepare a candlelight dinner. It would be even better if you can cook Western food yourself. If you can't, go to a Western restaurant with a romantic atmosphere. Otherwise, if you propose to him, he will feel that this birthday is more meaningful. It is not only boys who propose to girls.
You can give him a backpack. The latest design of the straps can reduce the weight on the shoulders and back, and it meets the user's requirements. A water bag is prepared, and the fabric of the bag is waterproof, which is very suitable for soldiers' daily use.