Best walkabout lens...Olympus have many to choose from. First off those kit lens (14-42) of your are fantastic piece of glass.
In the Standard range there is the 14-45, 18-180, 40-150(Mk1 and Mk2) and 70-300.
Then in the pro range, 11-22, 12-60, 14-54, 50-200.
Follow by the top Pro, 7-14, 14-35, 35-100, 90-250
Third party would include the
Sigma,10-20, 18-50/2.8, 55-200, 135-400 and 50-500 (think there are more)
Leica, 14-50/2.8-3.5, 14-50/3.5-5.6 and 14-150/3.5-5-6 (think need some editing on the f value)
These does not include the single focal primes.
So there is actually a whole lot of choices for you. Some shooters may even tell you a good walkabout lens is the 14-35/f2
but it still boils down to individual preference and the $$$$$ you are willing to burn for it.
For me, Leica 14-150 is now my current walkabout lens. It's almost glued to my camera.