(a) Drag your feet.
Dragging your feet works nicely in snow, when your brakes are frozen up and stop working. However, you have to dig in really hard to get much friction. On dry pavement, this is not so good because you feet get thrown back. On gravel and dirt roads it works well, but is a little hard on shoes.
(b) Turn into grass, ditch, etc.
When you're bicycling along out of control, with no or insufficient brakes, it's usually easy to pull off into the ditch (unless you're in the city), and the grass will slow you down. As you are coasting along in a ditch, you might be lucky enough to encounter a driveway which will slow you down really fast, although possibly not as fast as it slows down the bicycle. It's not too bad to bump into a chain link or privacy fence, but barbed wire should be avoided. You can also turn uphill sometimes, if there is room, and trade speed for elevation.
(c) Jump off (if necessary).
I have actually only jumped off in out-of-control situations rather than brake failures, but it does a nice job of stopping the bicycle driver if not the bike itself. This is difficult to do if you have your feet clipped into the pedals, and is not recommended at high speeds unless it seems really, really necessary, as in the case of a rapidly approaching cactus.
I have tried all of these.