After sunset on December 31st, families all across Japan will be sitting down to eat buckwheat noodles, which for the occassion are called TOSHIKOSHI SOBA ( literally, passing-from-one-year-to-the-next-soba).
This custom became widespread among the merchant class sometime during the Edo Period ( 1600-1868) . It was obviously a convient FAST FOOD, for the busiest time of the year, and this might be a major reason why this custom has remained so universal in Japan ( though there are some regions where other Toshikoshi dishes are eaten, and I might add that buckwheat allergies are not rare, and obviously families with sufferers would opt for something else).
However, just as with everything else that has become a staple of tradition in Japan, there is a symbolic significance in eating these noodles on New Year`s Eve. In fact there is more than one!
First, noodles are long and represent long life.
Second, buckwheat noodles break easilly, representing a clean break with the old year.
Third, in the Edo Period Japanese goldsmiths used buckwheat dough-balls to gather up gold dust from the floor or table ( which was then separated in water). Buckwheat therefore became a symbol for attracting gold ( wealth).
We can thus see that it is NOT only because they are convenient and delicious that eating soba on New Years Eve has become such a popular tradition!
( also remember that buckwheat noodles are presented to neighbors when moving into a new neighborhood. One reason for this is that SOBA, also means NEXT TO. Another is the fact that the noodles are long and slim, a way of saying, we are now close but lets not be THAT close.)
I have written more on SOBA here: