Bicycling and carrying...
Donut Guy--I think that Kilkenny nailed it:
Just leave it at home and don't exersize in gangland.
There are streets and roads everywhere. In Suburbia, and out "in the country," they are usually in better condition (i.e. the surface is flatter, with fewer unrepaired potholes) than downtown, anyhow.
Forgive me if I "just don't get it," but who in their right mind is going to assault a runner or bicyclist, anyhow--they won't have much on them in the way of cash or valuables, and they are likely to be in, at least, pretty good shape, therefore capable of mounting a better-than-ordinary resistance.
I carry "dog spray" on my bicycle--BTW, it DOES work--but anything heavier would just be an impediment.
IMNSHO, the greatest enemy of the bicyclist--and I have some experience here--is not the robber, but the inattentive automobile driver. In dicing with an automobile, the bicycle, right or wrong, always loses.
ETA--Back when I was a runner I also carried "dog spray." It will stop a Doberman pinscher in full-out attack mode, I was relieved to find. Scary.