We know that there are certain cards where you earn bonus points at supermarkets. In fact, you can learn a lot about these cards here.
However, be careful, if you are traveling overseas, some cards only offer bonus points when you use them at U.S supermarkets. It seems as if American Express rewards you for only food shopping in the good old USA. The American Express Gold Card, Amex Everyday Preferred, Amex Everyday, Hilton Honors American Express card and the Hilton Honors American Express Surpass card only offer the supermarket bonus in U.S supermarkets. The other cards, namely those offered thru Chase and Citi on the grocery shopping bonus list, reward you with bonus points at any supermarket.
Happy food shopping but not with your Amex!