As a general principle, Jewish holidays are divided between days on which you must starve and days on which you must overeat.
Many Jews observe no fewer than 16 fasts throughout the Jewish year, based on the time-honored principle that even if you are sure that you are ritually purified, you definitely aren't. Though there are many feasts and fasts, there are no holidays requiring light snacking. Note: Unlike Christians, who simply attend church on special days (e.g., Ash Wednesday), on Jewish holidays most Jews take the whole day off. This is because Jews, for historical and personal reasons, are more stressed out. The Diet Guide to the Jewish Holidays:

Rosh Hashanah -- Feast
Tzom Gedalia -- Fast
Yom Kippur -- More fasting
Sukkot -- Feast
Hashanah Rabbah -- More feasting
Simchat Torah -- Keep feasting
Month of Heshvan -- No feasts or fasts for a whole month. Get a grip on yourself.
Hanukkah -- Eat potato pancakes
Tenth of Tevet -- Do not eat potato pancakes
Tu B'Shevat -- Feast
Fast of Esther -- Fast
Purim -- Eat pastry
Passover -- Do not eat pastry
Shavuot -- Dairy feast (cheesecake, blintzes , etc.)
17th of Tammuz -- Fast (definitely no cheesecake or blintzes)
Tish B'Av -- Very strict fast (don't even think about cheesecake or blintzes)
Month of Elul -- End of cycle. Enroll in Center for Eating Disorders before High Holidays arrive again.