You can probably use the same 12V supply for driving your electronics. Just put a nice, big capacitor across the input to the regulator, close to the regulator. Something between 100 and 1000 microfarad would be good, and rated at at least 25 volts.
Also, you'll probably want to use a step-down DC/DC converter rather than a linear regulator like the 7805, to save some battery juice. Else you'll be burning off more power in the regulator than your electronics actually consume!