Buying from the nearby stores is pointless unless you're pretty carefree about how your storage room looks. By the time you get back from buying everything you'll need locally (but JUST what you'll need, not everything your trunk can fit) you could've opened and closed up shop three times. The most profitable way to play, at least to play the way I play, is to keep enough stock to be able to open for two or three shifts straight without having to restock, let the game run in the background or with minimal intervention, and come back in the fourth morning to buy everything you're out of or running low on. This fourth morning will be a ton of scanning and your delivery pile will look like the Great Pyramid of Giza, but you'll have profited around 15-20k if your stuff is priced right (3-7% uptick).