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. (Although you can invent your own e.g. the Extremely Reform Festival of the Pretzel Sticks.)

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 Yo-Yo 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)