I was told specifically to make them larger than twin size for wrapping up in purposes. It gets cold in the Fall and cold in air conditioning now (for those who have it).
I was also told to use non-military type fabrics as reminders of home are pleasing. Mentioning their service on the tag is appreciated so they'll have a service reminder when it goes back home.
I use a flannel back and Warm and Natural batting.
A general rule of thumb is to ask the recipient what they want. Some gifts are a hassle to deal with while deployed. It's best to get the okay first. That goes for general care packages as well.
My DF's blankets are always full size or a little larger. And, this time (Afghanistan) he asked for even bigger. He's getting an appliqued front and a pieced block back. No American military anything other than the signature block. I'm using an Army Star and a house block to bookend the siggie. Everything on the blanket has personal meaning.
I expected the first blanket I made to be burned upon redeployment. No big deal. I made it with that in mind. You burn your garbage when you leave. He brought it home and now it's in Afghanistan along with one other and one more on the way. I lucked out and got a blanket fiend.