What to draw with?

I'm still trying to discover what the "perfect" sketching medium is for me.
I keep a sketchbook and some oil pastels in the car if I want to do lunchtime sketching.

But to throw in my bag....
Even pared down to what I think is a bare minimum number of oil pastel sticks, it is still too bulky to throw in a medium-sized purse. So today I experimented with using just a pen and a pen with watercolor pencils.
That wasn't bad, I'll try it some more.