I always pack extra fluids, belts and filters in my 4Runner....I used to carry a set of new alternator brushes as well in my old Dodge Power Ram. Unsure about the starter, as stick shift trucks can be pull//push started...automatics not so much. Yours is a stick, right? I always carry spare U-joints. I imagine if you are doing some serious backwoods touring with your truck in deepest Africa, a new timing set and water pump might be a good call...but I wouldnt know how severe that job is on that engine. We dont get to have cool Toyota diesel anything here in the US.
I guess the moral of the story here would be "If you have the room and the need, carry it".