Best way to keep jambalaya warm?

In the oven covered with foil at about 225 degrees, in a disposable aluminum pan, if your oven will let you set it at that temp, if not the warm setting on it. If it is needed for timing issues a pinch of water added to the pan will insure the moisture level stays consistent with the steam it will generate.

If that doesn't work, you can line a cheap styrofoam ice chest with foil and it will keep it at serving temp for 4-5 hours if you put it in as soon as you cut the cooking fire.

A pre-warmed Yeti will keep it hot for days.

Electric roaster on the warm setting

2 hotel pans, steam, and a couple chafing fuel cans

Microwave works too.

Use an ice chest.