Buying food on Yom Tov

Purchasing food (that is necessary for Yom Tov) is permitted on Yom Tov, provided that a price is not mentioned and there is no transfer of money. If the seller is a non-Jew, it is also forbidden to show him where the buyer’s money is located so that he can take the payment for himself. Showing him the money gives the impression that a weekday activity is taking place. If the non-Jew does not trust the Jew to pay him after Yom Tov, one may give him an item as collateral. A Jew may not sell to a non-Jew on Yom Tov.

7 שו"ע תקיז, א ומשנ"ב ה; ביאורים ומוספים דרשו

It is forbidden to ask a non-Jew to do any act on a Jew’s behalf that the Jew is forbidden from doing on Yom Tov, even if the request was made before Yom Tov. Therefore, a non-Jew may not be asked to make a purchase in a forbidden manner (see above) for a Jew. If the non-Jew did make the purchase, the Jew may use the item b’dieved. If, however, the non-Jew has already done this twice or more for the Jew, the purchased object may not be used. The situation can no longer be considered b’dieved if the halacha was violated multiple times.  

8שו"ע תקיז, ג, ומשנ"ב ט ו־יא; ביאורים ומוספים דרשו

If a non-Jew performs a melacha for himself, a Jew may benefit from his action. According to some opinions, however, if he prepares a food which is very enjoyable, a Jew may not eat that food. There is a concern that the Jew will enjoy it so much that he will ask the non-Jew to make it on his behalf in the future. An example would be eating freshly baked bread. Others disagree with this stringency, and the Shulchon Aruch rules that under extenuating circumstances one can rely on the lenient opinion. According to some Achronim, this stringency only applies to bread that comes from a baker and not a shopkeeper. The concern about asking the non-Jew to bake the bread for him in the future would not apply to a shopkeeper, since he is not the one who does the baking.

שו"ע תקיז, א, משנ"ב ד, ו בהרחבה ע"פ המקור ו־ז, ושעה"צ ד