Some awesome advice so far...
If you're looking to make gravy (though you might not be, since you're planning on sandwiches...), I'd say simmer the neck in a quart of chicken broth along with one sprig of fresh rosemary, one bay leaf, and a few cracks of fresh black pepper. Let it simmer for a couple of hours, then pull out the neck and herbs. In a separate pan, make a roux out of 1/2 cup butter and 1/2 cup flour. Once the flour has just started to brown, and the whole roux takes on a "wet sand" kind of consistency, whisk in the broth about a cup at a time. Once it's all in there, cook down until it's the thickness you like, then shred the neck meat and add it back to the gravy.
If gravy isn't your thing, I'm totally with Fnjay about making turkey stock. Throw the neck, carcass, a cut up onion, a couple of ribs of celery, a dash of salt and pepper, and a cut up carrot in your Crock pot, cover with water, and let go on "low" overnight. Then remove the solids, strain, and save. Should freeze pretty easily, and will make preparations for Christmas dinner a whole lot easier - and tastier!
never tried this one but I always just toss the neck.
