The grill can be a lifesaver when you need extra oven/heating space on Thanksgiving. I've found ways to make use of the grill for just every piece of the meal, from mashed potatoes to brussels sprouts to apple desserts to turkey (of course). Even if you're not going to use the grill to do any actual cooking, it can still be an incredibly handy tool for reheating and warming various dishes when the oven is otherwise occupied. Here's how.
If you're looking to simply keep a few dishes warm, you don't need the same blistering fire you would to sear steaks or other heat-intensive tasks. That means you can start with significantly less fuel—around half a chimney full of coals on a charcoal grill or one burner turned to medium-low on a gas grill should do you just fine.
The Indirect Setup
Once you have those coals lit, you'll want to build an indirect fire, so no dishes will sit directly above the higher heat of the coals. To do this, arrange the coals in two piles on either side of the charcoal grate, leaving the middle empty. The area in the middle will be your indirect heat space for use.
A small fire will already give you a relatively low heat, but for reheating and holding, the 200-250°F range is a good place to shoot for. This requires restricting the airflow to the coals (or adjusting the burner if you're using a gas grill). On a standard kettle grill there are usually two dampers—one at the top and one at the bottom—that are used to control air entering and exiting the grill. Generally you want to leave the top damper open and use the bottom to control the airflow—the more it's closed, the less air comes in, and the cooler the fire will be. You'll probably need to fiddle with this throughout the day, so keep an eye on the grill temperature every fifteen minutes or so and adjust the damper as needed.
A good thing about a low fire is that it allows the coals to burn longer, so you can likely get a good hour or so of 225°F heat off of your limited number of coals. If you need to use the grill longer than that, it may be necessary to light up another batch of coals when you see the temperature start to drop and not respond to changes in airflow.
Maximize Your Space
Unless you have an incredibly large grill, you'll probably only be able to use the grill for a few casserole-style dishes. Luckily, you can maximize your space by adding and extra grilling rack. A product like the Hovergrill will do this in style, with a long legged rack that will fit a 22.5 or 26.75-inch kettle, but if you're like me, you can gerry-rig a rack yourself things like a few bricks or soup cans and an extra 18-inch grilling rack.
Keep it Covered
With the grill running low and loaded with Thanksgiving treats, it's best to keep that thing covered. Popping open the lid over and over again will allow the heat to escape, lessening the effectiveness of your grill holding station, especially if the weather is cold. So it's best practice to limit the amount of times you'll need to remove the lid, which will make the most out your fire and grill.