For one of his wife's Christmas presents last year, John Schroeder designed a calendar with photos of their family on (Stock Quote: HPQ).

The cost? About 38 cases of Coke (Stock Quote: KO).

Schroeder, 35, a software developer from Ann Arbor, Mich., accumulated points through Coca-Cola's rewards program, and redeemed them for the gift, which normally costs between $20 and $25.

Each 12-pack of Coke has a code that can be entered at for 10 points, and the cap from a 2-liter or 20-ounce bottle gives three points, but Schroeder didn't even have to drink that much soda. While keeping his Coke habit to two or three cans a day, he snagged boxes and caps from friends and family members.

"They don’t want to spend the time," says Schroeder, who estimates it takes him only about 10 minutes a week plugging in codes online.

These points programs are a small way to supplement your income by buying stuff you'll use anyway, though your time may be better spent nagging soda-guzzling colleagues to pass along their empties. People have been known to look through garbage cans or recycling bins, and some people trade bottle caps and codes online.

Coke gave away $70 million in rewards last year, according to company spokesman Scott Williamson.

Although credit card companies have recently been dialing back their rewards, it's not clear if the economy has had an effect on other programs. On Coke's site, Schroeder found more merchandise available at the end of the year than is available now, but he wonders if that was a lure for holiday shoppers.

"The plan now is to let (points) build up until the next holiday season," said Schroeder, who writes about the small ways he makes money on his blog, Passive Family Income.

After racking up enough Coke points, you can choose from among dozens of items, including $25 restaurant gift certificates for 280 points, magazine subscriptions for 100 to 200 points, and a car rental gift certificate for 650 points. You can also donate points to local schools.

Not all offers last, though, and some get more costly. Coke got rid of the AMC movie passes available a year ago for 220 points each, and a movie pass and soda combination went up 155 points during the summer before disappearing. If you see something you like, act fast, and check what’s offered before making the effort.

The company modifies the rewards according to feedback from its members on new things they'd like to see, according to Williamson.

The programs may also have expiration dates. Pepsi (Stock Quote: PEP) had a partnership with (Stock Quote: AMZN) that let people redeem points for electronics and MP3s, but the program finished at the end of last year, leaving some people with worthless points and bottle caps.

Other big companies with reward programs include Disney (Stock Quote: DIS), which lets you enter points available inside eligible DVDs, and get points for movie tickets.

Some programs are more rewarding than others, so choose wisely.

Stouffer's has codes on frozen dinners that can be turned into 20 points each through their "Dinner Club," and used to bid on big-ticket items like laptop computers and digital cameras, along with various $25 and $50 gift cards. You can also take online surveys to get more points, but the rewards are not guaranteed—you have to bid the highest number of points to win—so it's not the program for someone looking for instant gratification.

Schroeder and his wife have tried to amass points from Pampers (Stock Quote: PG), but at a half-point per box, their two sons didn't go through enough baby wipes to get a 100-point box of Cheerios. Coke also only lets you enter up to 10 codes per day, so it makes sense to use the 12 packs, which add up more quickly than bottle caps.

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