I am so sorry for your loss. Fighting back a hard cry as I write this. Our family is so fortunate that my brother was able to come back safely after 3 tours. I made him a quilt and was able to present it to him personally. I debated about what to do for him, as it was the biggest challenge I have ever taken on when quilting. I can understand the challenge you are facing.
What I did was think about everything He as the soldier means to me. I perused Quilters Cache looking for blocks that were fitting to his beliefs and what the soldier represents. I ended up using several blocks incorporated in the quilt. It was my own design, although there are several very good ones out there. I placed the blocks around a formation of a cross using patriotic fabrics. There are guidelines when doing a Quilt of Valor, and here is the link:
http://www.qovf.org/content/basic-qov-requirements.html. This might be a good place for you to start your planning. I did not follow all the guidelines, as I was presenting this to my brother in person. I did not go through the organization, but to me it is a Quilt of Valor.
A few of the many blocks I used are: A Soldier's Walk, Army Star, Honor and Courage, Sunshine and Shadows, Peace and Plenty, Our Country, Hearth and Home, Family Circle, Amerihearts at Home, Military Army Star, and God's Eye. It was a big undertaking, and it had a lot of work within the quilt. I used red, white, blue, and gold fabrics, but any one of these blocks could be made with military fabrics.
What I would do is keep it simple, yet reflect the soldier your son in law was.
I will keep your family in my prayers.