It's important to know the store coupon policy before you go on your next shopping trip. If you shop at multiple stores, you may well just want to print off the policies and keep them in your binder for quick reference. (you all got a binder right? :-) )
Each store has different policies, what they will and won't accept, etc. For instance - at Walgreens (and many other stores) you can not use more manufacturers coupons in one order than you have products. Now that seems reasonable enough - but many forget that the catalina's (register rewards they're called at Walgreens) are actually manufacturers coupons too - so when you go in to buy 10 items, and take 10 manufacturers coupons with you - they're not going to let you use last weeks' register rewards to pay for your purchase.
Plan your trip carefully so that you can make the most of your money and really stretch that dollar!