This list is reprinted with permisison from  Refunding Makes Cents .
Before you send in for that refund, are you sure you are sending the correct proof of purchase?
Some offers require that you send in parts of the packaging other than the standard UPC (Universal Product Code).  This is a list of many of those products.
There are times, however, when there could be two different offers on the same product.  For instance, the Correctol $2 Refund requires the UPC as proof of purchase while the Correctol Free Mug requires the box front.
So, to amend the old saying, When In Doubt...DON'T throw it out!
If you have anything to add to this list, please email  Susan Zennario .
Proof Of Purchase Required
Beggin Strips
Weight Circles
Butterball Turkey Products
Name and Logo from Packaging
Camel Cigarettes
Campbells Soup
Front Labels
Crystal Light
Foil Seals
Correctol Laxatives
UPC and/or Box Front
Dannon Yogurt
Foil Seals
Depends Undergarments
Proof of Purchase Points
Disney Videos
Stamps and/or Proof of Purchase Tabs
Doral Cigarettes
Oval Seal from top of pack
Enfamil Formula
Proof of Purchase Points
Francesco Rinaldi Sauce
Entire Label
Fuji Video/Audio Tapes
Proof of Purchase Stickers
Fuji Film
Kids In Gear Points
General Mills (Big G)
Boxtops for Education
General Foods International Coffee
Logo cut from plastic lid
Huggies Diapers and Wipes
Proof of Purchase Points
Icee Slush Drinks
Icee Chill Points
Kelloggs Corn Flakes
Corny Store Points
Kelloggs Cereals
Dated Boxtops
Kodak Film
POP U.S.A. Half Moons
Kool Aid Juice
Kool Aid Points
Kraft Macaroni & Cheese
Treasure Points
Maxwell House Coffee
Perk Points
Miniute Maid Frozen Drinks
White tear strips
Motor Oil - Individual Bottles
Tamper Proof Rings 
Motor Oil - Cases
Proof Of Purchase Seals
Foil Seal
Orafix Denture Cream
Orafix Points
Pepsi Points (Avail. only during Promotions)
Planters Products
Mr. Peanut Logo from plastic lid
Safety Seal from bottle neck
Poise Undergarments
Proof of Purchase Points
Pull Ups Training Pants
Proof of Purchase Points
Prestone Antifreeze
Foil Seal
Purina Cat & Dog Food
Weight  Circles
Quaker Oatmeal
Empty single packets
Sargento Cheese Snacks
Cow Chips
Sheba Cat Food
 Foil Pull Tabs
Slush Puppy Drinks
Paw Prints cut from cup
Smuckers Ice Cream Toppings
Front Label and Net Wt. Statements
Tombstone Pizza
Cactus POP Logos
Van De Kamps Fish Products
VDK Points
Winston Cigarettes
Proof of Purchase seals
WonderDry Diapers
Proof of Purchase seals