It is customary to use round Challot for Rosh Hashanah. (Some continue with this custom until Hoshana Rabbah - the last day of Sukkot.) I have heard that a circle, which has no end, signifies a long life as well as the ongoing cycle of the calendar. It also resembles the crown with which we coronate G-d as our King on Rosh Hashanah.
Following Hamotzi, one should dip the Challah (three times) in honey. It is customary to dip the Challah in honey during all the Rosh Hashanah meals as well as on Erev Yom Kippur, the night after Yom Kippur, the Yamim Tovim of Sukkot and Hoshana Rabbah. Some have the custom to dip the Challah in honey on all of the Shabbos and Yom Tov meals until Hoshana Rabbah. One should have salt on the table as well.
It was customary for the Chabad Rebbes to mention all of their holy predecessors during the Rosh Hashanah meals.
