When I catered for large parties with the full turkey, eight vegetables, two types of potatoes etc. I used to buy two turkeys. I would cook one the previous week and use the bones to make stock so that the gravy would be a minimum effort activity once the main turkey was cooked- I'd just add the stock to the gooey brown mess at the bottom of the roasting dish, give it a quick stir on the stove, and that would be it.
With a big kitchen and large chest freezer this sort of catering was easy. Now I live in a flat I am looking for space as well as effort saving techniques. While I was shopping today I noticed an array of ready-made gravy, thickened with cornflour. I decided to test this tonight with a roast chicken and vegetables.
This gravy can also be frozen. The one I bought today (Dec 12) had a use by date of Dec 27.