tuna noodle casserole going bad?!
It should be good for 5 days, roughly. You can get a thermometer for your fridge quite cheap if you are concerned. Optimum temp for cold storage is 35-38 degrees F. If it is as warm as 41, you are still in a safe range.
You can always freeze your leftovers. Don't wait if you are thinking about that. In the freezer, this will keep for 3 months. Label and date it, as you would anything going into the freezer. Frozen items are really hard to identify and remembering a date it went in, more so. You can get freezer bags and freezer tape at your local discount store.
About 5 days tops. If you have a Lot left then divide it up into indivudual portion sizes and Freeze.
Tuna casseroles lose their charm very fast. The next day is pushing it.
It should be fine to eat now or you should toss it..
most left overs are good for a week unless frozen