One of the biggest reasons you should never go to the store without your coupon binder is in-store specials. You could always call the store and ask before running there for a gallon of milk, but chances are the person at customer service does not know everything about what deals are going on.
These deals fly under the radar because they are meant to reward shoppers that were coming into the store anyway. Sometimes they are the sudden result of a manager realizing they have ordered too much of a product. They are not advertised, so there is no way you could have known about them before you hit the door.
You obviously cannot use coupons you do not have with you, so you just have to be disciplined about always at least taking the coupons to the car. It is much simpler to run outside than it is to run back home. Nothing is going to stink more than realizing you could have gotten 10 bottles of laundry soap for free.
Always make sure to check for limits on these deals, they may not be a part of your extreme couponing shopping trips, but they can be nice little side deals to build up your stash.