walkabout lens will depend on the kind of shot you like. If you are more into landscape then a wide angle like 10-22mm is good, if you like street and candied shot then a mid range like the 24-70mm for me as 70% of my shots are in this range.Of course a 70-200mm can do the job too for those who have strong arms and dont mind the weight, this rang can also be use to take your girl friend with a very nice bokeh 
