Usually, you can use those coupons on "sale" items, but you can't combine coupons. I scour the Sunday ads every week for what's on sale for 40-50% off. Since I can use my Teacher 15% discount on regular and sale items, I get an additional 15% off of the half-price sale, which saves me a ton!
I almost forgot about having that 30% coupon, so I'll have to decide what I'm gonna spend it on this Saturday.