Andy is spot on about discarding the food you left out overnight.
However, from your initial post, you mentioned
So, I was going to cut the rest of the chicken/meat and then cut up the veg. Pour gravy over it (thin it using some water) and then put in a pot and boil.
I think making a pot pie with leftovers like those is a great idea, but I wouldn't boil them They're already fully cooked. I would put the meat and veggies into the casserole, add the gravy, and then top with the pie crust. At this point, you could bake and then freeze, or freeze for later baking.