Have to agree with sm. If you can get the hell out of Dodge, run baby run. What I teach my students, anyhow.
If not able to flee, pepper spray with a stout OTN rating (just learned about "OTN").
Although spray is not effective 100% of the time, what one carries is a trade off between convenience, practicality, effectivenss and ease of deployment. Foam based spray seems to be the best bang for the buck (although I really do like the fire extinguisher type of powder for disuading several attackers quickly - if that situation even arises).