You wife (partner/friend) went to the shop to buy some food. She knew that among other things she had to buy some bread.
She has already returned home. You aren't talking to her about the shop or about any events of the past.
You only want to know if the bread is purchased, since right now you are hungry and want a sandwich.
What would be your most typical question: "Have you bought it?" or "Did you buy it?"
Thanks! (Please, name the country you are from, as it is really interesting if there are any differences between UK / US / Canadian / Indian habits of speaking). Thanks again!