Off the Menu
On Rosh Hashanah it is customary not to eat sour or bitter foods, e.g., pickles or horseradish. This symbolizes that we shouldn't have a “sour” year but rather a sweet one. Drinking hard liquor is acceptable (in moderation obviously).
It is also customary to refrain from eating nuts as eating nuts increases one's saliva which may disturb one's concentration in prayer. In addition, the Gematriyah (numerical value) of Egoz /nut is 17, the same numerical value as Chet/sin (not counting the “alef” which is not vocalized). Some refrain from eating these foods until after Hoshana Rabbah.
Grace After Meals
If one forgot to add Ya'aleh Veyavo (the holiday insertion) when saying Birkat HaMazon (Grace after Meals) after a night meal of Rosh Hashanah, one should repeat the Birkat HaMazon. If one forgot to say Ya'aleh Veyavo during the Birkat HaMazon after a day meal, one need not repeat the Birkat HaMazon.
Near the conclusion of the Birkat HaMazon, after Mimarom (Siddur pg. 93), we add the Harachaman for Shabbat, the one for Yom Tov, and lastly the one for Rosh Hashanah.
We say Oseh Shalom and not Oseh HaShalom at the end of Birkat HaMazon.
The prayer for Yom Tov: (Hu Yanichilaynu L'yom Shekulo Tov) should be recited before the one for Rosh Hashanah: (Horachamon Hu Yechadesh Aleinu Et Hashanah Hazot Letova Velivracha) as it is more common (tadir).
It is best for one to refrain from marital relations on both nights of Rosh Hashanah. One should not refrain if it is mikvah night.
