In many parts of Israel, everything closes for the Jewish day of rest, the Sabbath, but in Tel Aviv, this is definitely not the case. This is why you will find that a lot of places are open during the Sabbath as well, and even 24/7. One such example are the many smaller supermarkets that are open all day and night, every day (except for certain holidays, but there are very few of them), so if you are staying in central Tel Aviv, you can always count on being able to find a supermarket that is open no matter when you need it. The most famous 24/7 supermarket chain in Tel Aviv is the AM/PM, but there are several others as well. Keep in mind however, that these supermarkets do not sell fresh meat and fresh bread all the time (Tiv Taam being the exception) and that their prices are slightly more expensive than the ones in regular supermarkets. Most 24/7 supermarkets also only sell kosher food (again, Tiv Taam being the exception).