I'd estimate that only a small proportion of stations in NJ are attached to any convenience stores that sell things. On highways, yes. Off of highways around towns, they're often attached to a mechanic's garage, and the only things sold beside gas is windshield fluid and a spare quart of oil.
It's notable that NJ and Oregon both have cheap gas relative to many other parts of the country due to close proximity with oil refining &/or transportation infrastructure, which means lower costs to get it to the gas stations.
Although in NJ that discount is slowly going away as the state gradually ratchets up tax on gas purchases. Without that tax they would have by far the cheapest in the country by roughly 16% or $.50/gallon. Now NJ is only cheaper than most when there's a spike in oil prices stemming more from transportation costs, or at least that's what I've observed.
One consequence is that our state gas tax hasn't been raised in decades. That's why our gas is cheaper than across the border in WA. They pay a much higher per gallon tax than we do. My town has gotten around this by adding a $10 a month fee for road improvements to our water bills. Other cities and towns let their roads crumble.