I wrote this very same thing last year: for delicious turkey gravy on Thursday, make a quart of rich turkey stock today or tomorrow.
Here's what my plan is. I'm roasting a chicken for dinner and I'll also throw into the oven two fat turkey wings and cook them till they look delicious enough to eat. I'll put them in a pan and cover them with water (I may add the chicken carcass—haven't decided yet. The wings I bought weigh about 3 pounds (and cost less than $4). I'll pour in at least that much water, probably more, enough to cover them by about an inch of water in a snug pan. I'll bring the water to a simmer, then put the pan uncovered in the oven set low, 180 degrees or so, overnight. They can go for as little as 8 hours like this or sixteen, doesn't matter so long as the water isn't simmering, is hot but still.
Tomorrow, I'll add a large onion, two fat carrots, a handful of garlic, a couple bay leaves, a tablespoon of peppercorns, cracked, and a couple tablespoons of tomato paste. I'll bring it back up to a simmer then put it in the oven for an hour. Then I'll strain it, twice. First through a colander or basket strainer, then through a cloth.
I buy inexpensive handkerchiefs for the kitchen. I hate to buy cheesecloth that will be used once and discarded. Not only are they washable, handkerchiefs also have a finer weave than the stuff you find at the grocery store and so work better.
I'll chill this stock, remove the layer of fat on top. On Thanksgiving it'll be ready to go. While the turkey is roasting, I'll make a roux with rendered turkey fat and use that to thicken the gravy while the turkey's resting.
If you're the one making Thanksgiving dinner, start now and stay ahead of the game.