Congrats on the the Alice pack score. When I was still on active duty I liked the bigger pack because not only could I carry more if I had to, but I could rummage around in it and not have to totally unpack the thing to get something out of the bottom. If it was not packed full, I had enough room to just move things around inside the back.
On the top flap (Cover, what-ever you want to call it) is a pocket inside the cover itself, held together with Velcro. That little pocket in the cover came in very handy (so long as noise was not an issue) for carrying all sorts of little things.
One of the big pockets on the front is just big enough to carry a full roll of Air Force Form 1 (Toilet paper).
I can not remember what all the pockets and belts and stuff were for, but I know you'll find a use for them.
Definitely get the padded straps, you'll appreciate them after just a few minutes.
I gave mine to my nephew when I retired back in 2004. He thought it was the neatest thing going and was the envy of the boy scout troop.