I'll play your silly game, which tool is next?
Steps for truing stock.
Absolutely necessary. A flat face to work from, a reference face..
Joint (make flat and straight) one face (reference face) so you have something to true (reference) the remaining three sides to. Not to be done on a planer because the feed rollers will push out any warp and it will reappear as the stock exits the planer. For the same reason use very little down force when jointing.
Joint one edge with the reference face against the jointers fence. This will give you a straight edge that is at 90 degrees to the reference face. Also an edge to reference the next edge.,
Rip a second edge on the table saw with the reference face against the table and the reference edge against the fence. Try to do it on the jointer and it will give you a straight edge but not one necessarily parallel to the first edge.
Now you can plane the piece to a proper thickness with the reference face flat down on the planers feed table. Since the reference face is flat the planer has no warp to press out so the face being planed will be not only be flat but parallel to the reference face.
The jointer performs the two most critical steps in the process (the reference face and edge) but, with sufficient dicking around, there are work arounds. but, without the dicking around, the planer will not perform the functions of a jointer and the jointer will not perform the functions of a planer.