I think the rule book is clear on this that each step must be completed during the transportation phase, but ensuring this isn't to emphasize turn order can a player pass on expending a donkey tile to save their choices for later? Sometimes during the first round I don't wish to make a delivery so would also like to save my tiles but not sure this is legal.
As per page 14 of the manual, 8.0 Transportation Phase: Each step must be fully completed before the next step is started.
So my understanding is that it's a mandatory action/step. No savings.