Tomalley:
This is the green paste looking stuff you will find in the head. Technically it serves as a combination liver and pancreas. It looks somewhat like wasabi paste and often used in sauces.
Can I eat that part?
Yes, especially if you are a "fishy flavor" type person. Caveat: the tomalley can contain concentrations of toxins and pollutants (as all liver meat can).
Gills
Right under the body shell are the spongy, feathery gills wrapping around the outside of the body cavity.
Can I eat that part?
Not so much.
Roe
The eggs are called roe and are bright orange after cooking. They can be found in the tail and the body cavity.
Can I eat that part?
Indeed. Quite a treat.
Legs
Those skinny things they walk on.
Can I eat that part?
Yep, The legs contain meat but can be time consuming to get to. Pluck them off and suck the meat out.
Body
All that other stuff under the shell
Can I eat that part?
Yes, remove the lungs and the papery dividers. There's a good bit of flaky meat in there with a more crab like consistency.