As far as film types, among the more popular choices out there is 35mm, which is still widely available and is relatively easy and affordable to get processed. Not to mention, with a 35mm camera ...
The holiday is celebrated annually on March 5th, and aims to honor traditional film-making that happens on 35mm film. (Get it? March 5th, when written as 3/5 ... is 35, as in 35 milimeter film.