It is customary to eat red meat and sweet foods on the days of Rosh Hashanah, as the verse in Nechemia states, “Go eat fatty foods and drink sweet beverages and sent gifts of food to those who do not have, for the day is sanctified to our Lord.”
One may not fast at all on Rosh Hashanah. Nevertheless, one should not eat his entire fill so as not to cause himself to act frivolous as one must keep the fear of Heaven before him. Some customarily dip the bread eaten at the time the “Hamotzi” blessing is recited into honey or sugar. The Kaf Ha’Chaim writes that one should nonetheless dip the bread in salt as well, as he would throughout the rest of the year. Some customarily abstain from eating walnuts on Rosh Hashanah as the Hebrew word for walnut, “Egoz,” has the same numerical value as the Hebrew word for sin, “Chet” (without the Aleph). According to the Kabbalah, one should abstain from eating red grapes on Rosh Hashanah, however, this only applies to red grapes and not to green grapes; on the contrary, it is actually auspicious to eat green grapes on Rosh Hashanah. Some customarily abstain from eating any bitter, sour, or spicy foods on Rosh Hashanah. Similarly, it is written in a responsa of the Geonim that one should not eat spicy foods on Rosh Hashanah.
It is customary not to sleep on Rosh Hashanah day (such as an afternoon nap and the like), for it is not proper to sleep when the books of life and death are open before Hashem. Indeed, the Talmud Yerushalmi states that one who sleeps on Rosh Hashanah causes his fortune to be “asleep.” Thus, one should try to arise at dawn on the morning of Rosh Hashanah, or at the very least at sunrise, and carry out the appropriate preparations for prayer services. If one is tired and feels the need to sleep, one may sleep after halachic midday. Similarly, Rabbeinu Chaim Vital writes that his Rabbi, the holy Ari z”l, would sleep on Rosh Hashanah after halachic midday.
If one sits around idly and engages in idle chat and the like, it is considered as though he is sleeping; on the contrary, it is better for one to actually go to sleep than to sit around chatting idly. Some customarily read the entire book of Tehillim (Psalms) twice on Rosh Hashanah, for Tehillim consists of one-hundred-fifty chapters and twice this amount is equal to the numerical value of the Hebrew word for forgive, “Kaper” (three-hundred). The Ben Ish Hai writes that some customarily learn Tractate Rosh Hashanah with the commentary of Rabbeinu Ovadia of Bartenura after the festive meal on the night of Rosh Hashanah and this is indeed a fine custom.
Rabbeinu Yosef Haim writes furthermore in his Ben Ish Hai that one should take care not to become angry on Rosh Hashanah, for besides for the prohibition to become angry throughout the year, it is also not auspicious for one to become angry during these days. One should be careful not even to become angry in his heart. Thus, one must mentally prepare himself in advance to be completely happy on Rosh Hashanah, such that even if people anger him, he will be able to control his temper and not become angry.