That's doable,most stores in Japan are open till 8:00, a few seemed to stay open till 10:00 even. So you can sight see by day and shop at night. That's what I did.
I found the vending machines very convenient for basic stuff like water. there literally everywhere and cheaper than the convenience stores.
We have condom vending machines here, but their hidden away from the public in the mens room of pubs and clubs. I think is saw one or two Beer vending machines over there though, now that's an oddity by Australian standards. A beer vending machine in Australia would be asking for trouble.
Like the Simpsons episode where Homer get's his arm trapped in a vending machine.
Fireman: "Homer are you just holding on to the can"
Homer: "Your point being?"