Prices too. In my (limited) experience in the US, petrol stations charge a bit more for groceries than supermarkets, but convenience stores are significantly more.

Grocery stores typically have normal working hours. Petrol stations could be thought of to work 24 hours. Also ducking into a small kiosk for a snack is less of a hassle than a grocery store.

Is it just me or does this not make sense? It says you must declare the purposes of the processing for which personal data are intended, but this is under the section for when no personal data is collected. How does that work?