The holiday of Shavuot will fall out this coming Wednesday (beginning from Tuesday night), G-d-willing. In Israel, Shavuot is celebrated for one day and outside of Israel for two days, Wednesday and Thursday.
One is obligated to eat bread during all Yom Tov meals; both during the night and day meals. There is, nevertheless, no obligation to eat three meals on Yom Tov as there is on Shabbat.
In Birkat Hamazon recited on Yom Tov, one must insert “Ya’aleh Ve’Yavo” before the “Boneh Yerushalayim” blessing, as printed in Siddurim. This applies equally to Pesach, Shavuot, Rosh Hashanah, Sukkot, and Rosh Chodesh in that “Ya’aleh Ve’Yavo” must be inserted into Birkat Hamazon.
If one mistakenly omitted the “Ya’aleh Ve’Yavo” text from Birkat Hamazon, how one should proceed depends on several factors. If one remembers after having said the words “Baruch Ata Hashem” but before he saying “Boneh Yerushalayim”, one should conclude by saying “Lamedeni Chukecha” and then proceed to insert “Ya’aleh Ve’Yavo” (meaning that when has already said “Baruch Ata Hashem”, one should not end off the blessing by saying “Boneh Yerushalayim”; rather, one should recite the words “Lamedeni Chukecha” and then proceed to recite “Ya’aleh Ve’Yavo”). If one only remembers that one has omitted “Ya’aleh Ve’Yavo” only after concluding the blessing of “Boneh Yerushalayim”, one should recite the following blessing: “Baruch Ata Hashem Elokeinu Melech Ha’Olam Asher Natan Yamim Tovim Le’Yisrael Le’Sasson Ul’Simcha, Et Yom Chag Ha’Shavuot Hazeh Et Yom Tov Mikra Kodesh Hazeh, Baruch Ata Hashem Mekadesh Yisrael Ve’Hazemanin.”
If one has already started the fourth blessing of Birkat Hamazon (the blessing of “La’ad Hakel Avinu Malkeinu”), i.e. one has concluded the blessing of “Boneh Yerushalayim” and has already begun to say “Baruch Ata Hashem Elokeinu Melech Ha’Olam” at which point one immediately remembers that he has forgotten to insert “Ya’aleh Ve’Yavo”, one should continue with the text of “Asher Natan Yamim Tovim” (see above), and following that, one should begin the fourth blessing anew.
If one remembers that he has omitted “Ya’aleh Ve’Yavo” only after reciting the words “La’ad Ha’el Avinu Malkeinu,” one can no longer remedy this and make up the “Ya’aleh Ve’Yavo”. There are situations where one must repeat the entire Birkat Hamazon and there are others where one does not, as we shall explain further in the following Halacha.
