As i have lived in Brazil for many years and been countless times to the supermarket, this puts me in good stead to give you a few home truths about shopping in Brazil.
First of all there isn't currently a shortage of any domestic item in Brazil that i can think of.
Prices do vary however, for example expect to pay a little more for goods at the corner shop than you do at the supermarket, as you are paying for the convenience and to be honest the supermarkets *** in bulk where upon the corner shops *** in a few boxes.
Be prepared to get onto a line in a supermarket, and have plenty of patience.
Try and visit the supermarket during office timings as there will be less people there, very good tip.
A lot of people now take their own bags to the store as in some places they will now charge you for plastic bags to put your groceries in, so be prepared. It may not be much for the plastic bags but if you have lot of shopping it could quickly mount up and usually does.
It always surprises me that every month it always seems to be more expensive for general house hold items, the prices are rising on a regular basis so look out for bargains and offers which almost all larger stores have. Will certainly save some cash for sure.