Like they said... brakes. Lower gears are easier to stop and start with because a lower gear = more mechanical advantage. But you'll also max out your RPM's sooner, too. In any case though, you need to have a brake that operates on your FRONT wheel as well as the rear. The drivetrain can count as one for the rear, but not for the front. You have more stopping power in the front, and you have more stopping power and more control when the wheel is rolling, not when it's skidding. In short, a front brake gives you a shorter stopping distance than skidding the rear wheel. If you are on a steep hill and the road is slippery (wet, sandy, oil from cars, etc) and you've gotten a moving start, it is entirely possible to skid the rear wheel for a whole block and still not stop, where a front brake could actually stop you. SF has steep hills and I think it rains their occasionally.
So yeah, brakes.