According to Halacha, one should not eat a meal before hearing the Shofar blown. Many such as rav Yosef Eliyahu Henkin were Machmir even when it comes to drinking. The source of this general principle of not eating before a mitzvah is in the Talmud of Masechet Sukkah. My question is, can a Kohen eat and/or drink before Birkat Kohanim?
Nitei Gavriel, Hilchos Yom Tov 60:9 says it's forbidden to eat a meal and it's best not to eat at all:
אנשי מעשה נוהגים שלא לטעום מאומה קודם נ"כ, ואכילת קבע אסורה לכו"ע