Lots of good answers, especially regarding how easy it is to get a pop-up if
you already have flight following. I'll just add one more item - fly a route
you could fly IFR with the equipment you've got. For example, while my
handheld GPS can take me direct anywhere VFR - I'm screwed if I need an IFR
pop-up and I'm not on an airway in my VOR only equiped plane (/U). So I
pretty much always follow airways - just on the off chance I need to
"convert" my flight following to an IFR clearance.

-Brenor