*The following may surprise the reader and/or contain sarcasm. The reader is responsible for his or her own actions and cannot hold the writer responsible for any negative feelings this answer may arouse in them*
That is a very broad question. Obviously no one can tell you exactly what will be happening on December 21st, 2012, but one can guess based on what they observed.
I'm almost sure that I will brush my teeth at least twice, have 3 meals during the day (or it's equivalent), waste time looking up random stuff on the internet that doesn't matter (until I decide to write a hub about it), possibly go sky diving, and many other things anyone would do on a day to day basis.
Whether the world ends or not is none of my concern, because I know it won't be ending on December 21st 2012, or ever. I can say this with complete confidence, because if by some chance I'm wrong, we'll both die and it won't matter anyway.
So I'll be sky diving.