a can of mace in your pocket (never in your bag, it's harder to just grab and use in an emergency situation)
if he's lying down, stomp on his ankle with full force
personal alarm device is a great addition, a sudden loud noise is confusing and distracting, while also alerting people around who might pay attention
same thing with a taser, the sound alone is intimidating as hell
don't carry a knife or other tools like this if you're not absolutely, completely 100% confident in your fighting skills with it - it's easy to take away, you can even accidentally drop it, and it could be used against you
comfortable shoes can go a long way - personal confrontation is a last resort situation. run for your life if you can
never tuck your thumb inside your fist - lay it over your fingers instead. you don't want to break it
if you have to, you can harden your fist by putting a matchbox inside - keys and other hard object are highly discouraged. matchbox is easy to carry and can give your punch a stronger blow
your elbow hook is absolutely capable of breaking a nose
do literally anything it takes to get out of this situation. use what you can to your advantage. keys on a chain as a whip, pens, nails, teeth - anything. don't be afraid of taking action
once again - groin, eyes, neck, nose, stomach. they also have vulnerable spots, remember them and act, if it comes to it