Okayyyyy...
Chapel Market is fine, but Ridley Road in Dalston is better, and has a bigger range of fruit and veg. At the far end (away from Kingsland High Street) they have stalls selling big bowls of fruit for a quid a go. There are little shops along the market selling all sorts of ethnic stuff, so if you want a pickled pig's tail, or cow's foot, someone will be able to supply you. There are good fish stalls there, too, though I steer clear of the cheapo butcher.
Also at the far end of Ridley Road is the Turkish Food Centre, which has great fruit and veg, olive oil, pulses, spices, and lots of foreign-y stuff like olives, white cheese and spicy sausages. The place is a treasure trove, and no more than 20 mins walk from you (or 38/56 bus to Dalston Junction, if you're feeling tired).
Even nearer to you is James Elliot (butcher) on Essex Road, and Steve Hatt the fishmonger next door. Neither is particularly bargain basement, but they're not snotty if you go in and say, "I need a cheap lamb joint to make stew" or whatever.
For bulk buying of standard groceries, there is a Lidl in Well Street, off Mare Street. We're car-less, but I do a monster shop every six weeks or so and bring it home in a minicab.
hth