I didn't understand it until I did some research, but the reason that they buy so many of a particular item is because sale prices go through phases. More sophisticated couponers watch sale prices and keep a track of "rock bottom" prices, so when something you buy gets to or below your rock bottom price (which for many means with the use of a coupon they pay little to no money) it's time to stock up. 

You buy a lot because it will be a while before whatever item will get to your rock bottom price again. I don't think they tell you that on the show, but that is why people keep a stash or stockpile. These people aren't buying things to fill their pantry every week, they buy when the things are little to no cost and keep a good amount to last. So they may go to the grocery store and only get 10 things, but they'll buy a sh*tload of those 10 things to last until it gets to rock bottom sale price again. And this is repeated basically weekly.

Don't be loyal to one store. And sign up for store cards with your correct address. Many of them will mail you store coupons directly which can be used on top of manufacturer coupons (stacking) or total purchase coupons.

Another thing-some stores won't give you overage (I think wal-mart may be one) so like mentioned you have to be very aware of store coupon policies. One's that do give you overage-that can be used to buy (fresh) meat, seafood, veggies and fruits. Almost anything else in the store you can get a coupon for.

I've gotten many free things, and some for low cost. I've gotten free cake mix, lotion, hair conditioner, milk, and other crap. And many, many things for low cost-cereal is a big one, yogurt, juice, makeup, and again many many other things.

do you work? if so you can get food stamps 

also look out for stores that give discounts for students 

the grocery store closest to campus here gives 10% off your purchase if you come in wearing your school colors 

You can! If done correctly you can use the overage from items with coupons on non coupon items.

And what does that mean???

has these huge coupon books that cost $25 but the book will pay for itself.

It has coupons for grocery stores, clothing stores, and dining for most areas. 

I find them really helpful.

Doubling a coupons means the place that accepts it will match the price of the coupon (usually up to $.99)

For example, you want a bag of chips that cost $2.00 and you have a coupon for $.50

The place will take  an additional $.50 off and you pay only $1.00 for the chips