Don't forget raking your instep down the shin as you go to stomp on the other person's instep. Hard sole edges work better, but even sneakers can hurt.
If you get into a chest-thumping, belly-bumping situation and can manage it, clapping them on the ears will cause a world of hurt. Big, wide arm swing or start with the arms close together as if to break an armhold attempt then open up enough to get the needed width. Flat hands seem to work better than cupped hands. Do it hard.
Thrust extended knuckles of first 2 fingers into the adam's apple/voicebox.
Use elbows instead of fists whenever possible - less chance of injury to you.
Do not forget that pens, keys, books (hardback or softcover), hairbrushes, those stubby antennas on some cell phones all make excellent stabbing devices. Books also are shields.
Depending on how heavy/bulky it is, a backpack can make an expedient flail.
Punting/drop-kicking the huevos may not be the best way to attack. Too much risk of either getting the leg trapped or losing balance, or worst of all hurting your own foot. If you are going to do it, use the middle of the shin instead of the instep.
Kicking/stomping the side of the knee may be viable. Depends on a lot of variables.
Perhaps buy this book
http://www.amazon.com/womans-guide-personal-defense-street/dp/0399518452 stay safe.
