When all I had was my M2 and a 35mm Summaron, it seemed to be all I needed. But then I added a 90; and then a 50; Then a Nikkormat with 55mm micro-Nikkor; and a Hasselblad with 2 lenses; a Rollei; well you get the idea.
Most of the time I like to have more than one focal length available. If going light, a pocket size digital P&S works great. If I want to go with one camera and one lens, it's either a Leica with a 35mm, the Fuji X100 (essentially 35mm), or a small P&S with a zoom. The advantage is convenience and readiness for a shot, with little or no equipment fiddling.
May the light be with you.