You know those little acordian file looking things, just a little bigger than a checkbook? That's what I use. I labeled each tab: Food, bath, cleaning, kid stuff, Misc, and "going out" (restaurants, Chuck E Cheese, etc).
On Sundays I cut the coupons, sort them, stick them in the correct tab by date of expiration. If I am not going to use a coupon before it expires, I don't cut it or keep it. If it's expired, it goes in a trash can. I "clean out" my coupons the night before going to the store: is there something expiring soon that I don't really need? Trash. Is there something I'd like to use on my shopping trip? Pull it out, put a little * mark by that item on my shopping list, meaning that I have a coupon for it, and put it in my wallet. Coupon file stays at my desk. I put the coupons and shopping list in my purse (or diaper bag) before leaving to go anywhere.