I bought an accordion-style coupon folder with a band around it at the dollar store for a mere buck
It didn't have any categories, though, so I made tabs for it: beverages, frozen food, toiletries, cleaning supplies, canned food, breads, seasoning, cereal, dairy, snacks, oil and dressing, and meats. I have the tabs staggered so each category's easy to see, and I have the coupons in each section organized. It neatly fits into my purse.
The only "down" side is that the thing is so tattered and worn, I've got to get a new one. I used my graphics software and fancy fonts for all the categories so that it's fun to use (gotta make my "inner kid" happy)...