Deer roast 5 hours in the crockpot with celery, mushrooms, and carrots, made brown gravy with the juice. Large slice of roast with celery and mushroom piled on with gravy on top, mash taters were to clean up the extra gravy. Good meal on a cold day!
I put some salt, pepper, garlic powder, onion powder on the roast, 2 cups water, added vegetables with 3 hours left.
Gravy was 2 cups juice from the crockpot, 2 tablespoons butter, corn starch to thicken.
It's pretty hard to mess up a roast in a crock-pot. Just some salt and pepper and some sliced onions and a couple of cans of crm of mushroom soup with some extra mushrooms, canned or fresh makes no difference.
That's about as simple as it gets. You can experiment with any other ingredients you like as well.