Almonds, a baggy full of vegetables, a kashi granola bar, or a piece of fruit.

Another vote for fiber one bars!

I keep LARABARS, Odwalla bars, and nuts in my purse... just in case.

Grapes! Two cups (enough to fill the biggest cereal bowl ever) is only 120 calories. I prefer them frozen, but they're also good in their standard form.

I don't carry a purse but I always have nuts, seeds, chips in little baggies in the car, I also keep water handy.