You can use just any bits of meat you have on hand to boost your jarred sauce, but you should reach for the fattier cuts of meat rather than a pork loin or chicken breast. Fatty meat will add some texture to the store-bought sauce, as well as introduce those excellent umami flavors that mimic a long simmer.
Fat is where the flavor is, and anything meaty, greasy, and cured will go really well in the sauce. Try to find fattier cuts, like pancetta, prosciutto, or even guanciale, but bacon will also do the job. Simply crisp it up, and keep as much of the rendered fat as you’d like in the pan before adding your sauce. Ground beef and Italian sausage are good here if you don’t have any of the fattier cuts of meat. No matter which one you choose, brown the meat in a skillet. The meat should be browned and have a crust where it touches the pan. Once that’s happened, break up the meat into chunks. You can leave some of the rendered fat and add the jarred sauce, then simmer. If you find yourself with some extra time, use that rendered fat to sauté some garlic, onions, or veggies to elevate the sauce even further.