I wish I could change the world for the better and "more efficient," all at once. If you implement my idea, I'll give you a cookie.
There's no technical reason that magnetic cards cannot identify themselves as "debit," "credit," or "gift" cards. Add card-type identifiers to magnetic stripe data. This would eliminate a confusion/nuisance step in payment at lines in all supermarkets across America, and probably save everyone a small amount of money (and annoyance).
Also, if you're a bank, give consumers an option to include a "telephone number" field inside of magstripe data that can be used (legally) to identify customers for coupon programs (e.g. Safeway Club, Von's Club, etc.). Allow customers to opt-out if they don't want this "vendor field" identifying them. Why not simplify everything into one easy step at the supermarket?