They are not all that generous, but you will not leave empty handed. Go to your local newspaper-recycling center and see if they will let you skim through and take out all the coupons other people tossed. I have done this, and, believe it or not, lots of people toss them out. You can even save the ones you do not use for trading purposes. Go to the post office and get yourself a bundle of plain, postage pre-paid post cards.
All manufacturers print their addresses on their products.
Write them and address the post card to their consumer affairs department, and comment on the product. You may get a thank you note, and maybe a coupon or so from them. One of my best experiences was to contact Lipton and comment on their iced tea mix. I got three coupons off the purchase price. Another great find is Valupage.