Tomorrow is December 1. There are 31 days left in the year.

30 is --
30 is the sum of the first four square numbers: 1+4+9+16
5 x 6; half of the base for the decimal system x half of the base for the duodecimal system = half of the base for the Sexagesimal system (Sumeria, Babylonia). Distributive law at work. There is a lot here but I won't get into it.
30 is zinc
30 is reporter and editor code for end of story
30 is the minimum age to be a US Sentor