Surely you know of at least one purim carnival or event going on this weekend somewhere in the City. If not, ask any friend! and drop off your used books as you arrive (see my post below)
But one place where you can see something really unique and free this Sat. is the JCC. You can still go to the synagogues in the morning for services, the evening for the Megillah reading and Sunday for carnivals and shows galore!