Why does it say "Zos Asu"?
Ohr ha'Chayim #1: This (loading your animals) you may do without permission. Taking wagons (45:19) was a command. It is a law of Egypt [that wagons may leave only with the king's permission - refer to 45:21:151:1].
Ohr ha'Chayim #2: Pharaoh himself suggested that they do so, not that he merely consented to do Chesed for them. It was from Hashem, so that our ancestors would descend to Egypt.
Malbim: Yosef has authority to tell his brothers to load their animals, but only Pharaoh can authorize taking wagons; refer to 45:19:1:5.
What is the meaning of "Ta'anu"?
Ibn Ezra: Load them. 1 This is like "Meto'anei Cherev" (Yeshayah 14:19). 2 Malbim (to 45:21) - Ta'an is a light load, unlike "va'Ya'amos" (44:13). You do not need all the grain, 3 only what the animals will eat on the road, for you will return immediately! Their animals are called "Be'irchem," for this is used regarding animals eating - "v'Shilach Es Be'iro u'Vi'er bi'Sedeh Acher" (Shemos 22:4).
Ba'al ha'Turim, Ha'amek Davar: [Lightly] stab them, to make them go quickly. This is like "Meto'anei Cherev" (Yeshayah 14:19).
Ba'al ha'Turim: This is not so. They need not load the donkeys; the wagons can carry what is needed! See 45:17:152:2.
Malbim (to 45:21): That verse means, 'they were killed via people bearing swords.'
I.e. the brothers had bought enough grain to feed their families for a while. (PF)
QUESTIONS ON RASHI
Rashi writes: "'Load your animals' - with grain." How else might I have understood this?
Gur Aryeh: I might have translated that the animals should themselves be loaded onto something else, which would carry them.
