Two things:
First, the boardwalk does have a rear brake - a coaster brake (just pedal backwards).
Second, developing the ability to brake well depends on being able to use your front brake properly. Under most conditions the front brake provides the vast majority of your braking power. On an upright folding bike this is slightly less of a factor than on other bikes, but it still holds.
Read:
http://sheldonbrown.com/brakturn.html
That's not to say that you can't stop by using the rear brake primarily, but that if someday you need to stop on a dime due to an impending accident it would be good to know how to properly use your front brake.