Buying a bike this year has saved me lots of money on food ('cause I can purchase things outside of my overpriced area).
I try to shop for most regular things at Associated Market on West 14th , Key Foods (Ave A) or Western Beef on West 16th and even Metro Drugs (!) because they're all very cheap and all very clean.
Here are some bargains they I get at ordinary markets...Frozen (gasp!) pre-sliced store-brand small-ish frozen onion bagels (six to a pack) are usually about a $1.00/pack. I keep lots of these at home, freeze 'em and toast each one as needed, smear it with Philadelphia Salmon Cream Cheese, Sliced Red Onions/Capers and voila...a pimped-out bagel on the cheap! These bagels are good when lightly toasted, they still have that "bounce".
Western Beef store-brand Cereals...Apple Cinnamon Toasted Outs (they taste like Apple Jacks but they're made with Oats). They also make faux-Captain Crunch and other cereals that are now too pricey.
Frozen Potato Patties in a pack of 10 lined up in row (you've seen them)...great with a poached egg on top, manchego cheese, beans, etc.
Gourmet stuff I'll get at East Village Cheese Shop, Kalustyan's, Holy Land Grocery, National Wholesale Liquidators (used to be better) or go to Brooklyn/Queens. For Fruits/Veggies - it's Chinatown.
Oh yeah, a large pack of Sugar Wafers (0.59cents/each at Metro Drugs), with a glass of cold milk - it's a cheap thrill.
Do you have any cheap foodie supermarket finds?