If he's served 3 tours, you can bet the military is near and dear to him. I would suggest giving a donation to the FRG (Family Readiness Group) for his unit. This is the group for the families of those who are serving and they do all sorts of things to help prepare the soldiers to leave, keep their spirits up while they are gone and then welcome them home and reunite them with their loved ones! Every unit has one.
If your daughter knows what unit he was in, a little research to find contact info for his unit would get you to someone who would know how to connect you with his FRG. It would be such a nice thing for him...and it would reflect so positively on him, amongst his military peers. It also will make him proud that your donation will be helping his buddies and their families directly...those that served beside him and are still finishing their tours.
If you can figure out his unit and want help researching the contact person for his FRG, I would be happy to help. I was involved with my husband's FRG here in Orlando a few years ago and I believe I still have my resource directory.
God bless you for making this effort, whatever you decide.