Based on what Tristan is doing, he is most like the Golgi apparatus. This is an organelle that is found in almost all eukaryotic cells, and whose main responsibility is packaging proteins into membrane-bound vesicles inside the cell which are later rerouted by the vesicles to their final destination. Which is almost exactly what Tristan is doing as he is preparing the gifts (proteins) and takes them to the post office (vesicles), which they will then take to the packages' final destination.
