What is an adjective that means "fits the norm"?

You can try standard (as in standard practice):

Used or accepted as normal or average.

(source: Oxford Dictionaries)

As far as English language usage goes, it's actually perfectly fine to say "normal" in this case.

Saying "the normal celebration" refers to one definition of the word normal which means precisely "conforming to the norm." The use of the definite article implies that there is a single norm and you are talking about that specific thing.

There is another definition of normal, which simply means "not abnormal." That is the definition used to describe Hanukkah in your example.

In America, the normal midwinter celebration is Christmas. It is also perfectly normal to celebrate Hanukkah.

There are a few other words I can think of that would fit into your blank:

• typical
• usual
• standard
• customary
• traditional
• conventional