Those who observe a fast on Ereb Rosh Hashanah should preferably refrain from meat and wine the night before Ereb Rosh Hashanah. The idea of a fast is that the body fat and fluids which one loses by abstaining from food and drink for a day are viewed as a sacrifice to G-d, and thus if one indulges in meat and wine before the fast, he will not have lost anything. This resembles the comment made by Rabbenu Abraham Ben Ha’Rambam, cited by Hacham Bension Abba Shaul (Israel, 1923-1998) in his Or Le’sion, condemning those who gluttonously indulge before the fast and spend the fast thinking about the food they will eat after the fast. As this is inappropriate, it is preferable that those who fast on Ereb Rosh Hashanah avoid meat and wine the night before.
If one had accepted upon himself to fast on Ereb Rosh Hashanah, after he goes to sleep for the night he may not eat or drink, even if he wakes up before daybreak, unless he stipulated before going to sleep that he still intends to eat and drink. This is the view of Maran in the Shulhan Aruch. The Rama (Rabbi Moshe Isserles of Cracow, 1525-1572), however, maintains that one may drink if he wakes up before daybreak even if he had not made a stipulation before going to sleep. It should be noted that for a private fast, such as the fast of Ereb Rosh Hashanah, it suffices to make this stipulation in one’s mind; one does not have to verbalize his intention to eat and drink.
The Zohar took a different view, and maintained that once one goes to sleep for the night, he may not eat or drink before praying Shaharit. One may, however, drink water, tea and coffee, even according to the Zohar, and even if he did not have this in mind when he went to sleep for the night. Other beverages, however, such as milk, wine and beer, are forbidden. In light of the Zohar’s ruling, Hacham Bension Abba Shaul ruled that if one will be unable to fast unless he wakes up before daybreak to eat, it is preferable for him not to fast. Fasting on Rosh Hashanah is not strictly required, and one should not violate a ruling of the Zohar for the sake of observing this voluntary practice.
Needless to say, if one wakes up early in the morning to drink before the fast, he must keep an eye on the clock to make sure he finishes drinking before the onset of the fast.
One should make a special effort to arise early in the morning on Ereb Rosh Hashanah for the recitation of Selihot. Although "Yehi Shem" is recited in place of Vidui and Tahanunim during Shaharit on Ereb Rosh Hashanah, nevertheless, Vidui is recited during Selihot that morning, even if the Selihot recitation extends past sunrise (Mishna Berura).