You would not use your 9×13 pan at all!
We know it’s a pain to chase your dishes down (especially if you use that pan often yourself). If you are making something for the casserole drive, sign up and then make the casserole(s) in the disposable aluminum pan provided by the BSC. You can pick up the pan at the BSC at 104 Faculty Street, Blacksburg.
Or, if you found this opportunity through your local church, check with your church contact – they may have the pans available.