Overheating is one of the more common problems I see listed for the Model A, but no one has mentioned carrying a spare radiator!
A spare fan belt, points, condenser and coil should get you home. As mentioned, all those spare heavy parts aren't needed, and if they were, then the Model A wasn't prepared for the trip in the first place. Most of the roadside repairs I've heard about or helped with have been due to lack of lubrication or lack of proper restoration of each part.