Nothing wrong with just bombing around... it's good for morale. But even after you get your ticket, you may want to select at least one maneuver or task before you take off, and make sure you do it before the flight is over.
I'm not opposed to students making solo flights practice flights, covering all the PTS stuff (that can actually be fun, too, and very very satisfying if you find yourself doing a good job), but if you feel like just working on straight & level and looking around, that probably means you need that today.
My rule of thumb, even today after exercising my "license to learn" for a couple hundred hours, is to consider, before I take off, what thing I could stand to work on most ( something I wasn't happy with on the last flight, or something I just haven't done in a while). Then I will just make a note to do that at some point, even if it's a trip from A to B.