Not sure why the zip code matters but we used a Land's End Featherweight Medium.
My DS is tall though, he was just under 4' when he started K.
It is in great shape and we will be able to use it at least one more year. They don't carry much in K. A lunch bag, the occasional library book and the Friday folder.
There were several kids with character backpacks (think minions for boys and frozen for girls) but I think a classic backpack makes the most sense for longevity. DS grows like a weed so the only thing from K he'll be taking to 1st is that backpack.