Strange, because you'd think such WIDELY celebrated holidays all falling together would have caused chaos with crowded stores and traffic jams.
What food could be served for such a day? Well it should be possible to make something that is a cross between a pie and a hamentaschen. And make it with berries and seal fat.
Purim is the 14th day of Adar. Pi Day is the 14th day of March. Inupiaq day is, I think, the second Monday in March.
In addition to these 3 holidays, it was also Einstein's birthday. But Einstein's birthday always coincides with Pi Day. Sort of like Boxing Day and the first day of Kwanzaa.