Don't give him a bone! If he is aggressive with food you will have problems and if he gets a bit stuck in his mouth you will have MAJOR problems.
How long have you had him?
You will find this link interesting and may give you some tips, it is about a GSD with similar problems to yours:
http://www.druidalegsd.karoo.net/shadow.htm
I would start off with food, get him to come to you for food.
I would also, if you can, get him checked out by a vet asap.
DO NOT ever back him into a corner, make sure he can get away from you at all times. That is why he bit when he was in the crate, what other option did he have!
This will take alot of time and effort, as in the above story. That lady is an experienced dog trainer/breeder and has lots of other GSD's and she came to the point of putting her GSD to sleep.
Good luck, I really hope you succeed, if you feel you are not up to it please, please get help and possibly rehome this boy to someone who knows what they are doing.