1,060. Forgetting an Eiruv Tavshilin Before Two Days of Yom Tov

Shvisas Yom Tov 6:11

When the two days of yom tov observed outside of Israel fall on Thursday and Friday, an eiruv tavshilin should be made on Wednesday, the day before yom tov. If one forgot to make an eiruv before yom tov, he should act as follows: He deposits an eiruv tavshilin on Thursday (the first day of yom tov) and says, “If today is yom tov and tomorrow is a weekday, I will cook and bake for Shabbos tomorrow, and there’s no need for me to make any special arrangements. If today is a weekday and tomorrow is yom tov, then through this eiruv I will be permitted to bake and cook tomorrow, which is yom tov, for Shabbos.”

Shvisas Yom Tov 6:12

Similarly, if a person has two baskets of produce from which terumah has not been separated, on the first day of yom tov he says, “If today is a weekday, let this basket be terumah for the other. If today is yom tov, then may my words be of no consequence.” He designates the produce as terumah and then leaves it alone. The next day, he returns and says, “If today is yom tov, then may my words be of no consequence. If today is a weekday, then let this basket be terumah for the other.” He designates the same basket and continues to leave it alone just as he did the day before. He may then eat the produce in the other basket.