One of the challenges to saving money through promotions and loyalty programs is the promotions and programs change frequently and sometimes unexpectedly.

Of course, the goal of many promotions is to get people used to buying a product or patronizing a particular business, and then to pare back the discounts while keeping the customer. For thrifty shoppers, the trick is to keep up with changing rules, and adjust shopping behavior in response.

For example, one of my long-time favorite promotions, the discounted gas cards offered by Harris Teeter grocery stores, saw a significant change in recent weeks. For several years now, shoppers with a loyalty "VIC" card have been given the right to buy a $25 Shell or BP gift card for $20, every time they spend $40 at Harris Teeter.

That might not sound like a big deal, but do the math. My wife and I have been buying gasoline for 20 percent off, every time we fill up, for years now, saving about $450 annually with that promotion.

The rewards would accumulate - if you didn't buy a gas card right away, your grocery store receipts would keep track of how many you could buy. Those potential redemptions always had expiration dates, but they never seemed to expire, until now.

In the past few weeks, Harris Teeter zeroed-out rewards more than 30 days old. Like many shoppers, I had grown complacent, allowing rewards to accumulate until I ran out of gas cards, instead of redeeming them for gas cards that don't expire.

While the gas card promotion continues, now shoppers need to actually buy the cards within 30 days of earning the reward.

In a different example of how shoppers need to adjust behavior to respond to changing promotions, consider coffee. Regular readers of this column know that I'm a pretty thrifty guy, but Starbucks coffee is one of the small luxuries I enjoy.

For a long time, if you purchased bagged Starbucks coffee at a grocery store, rather than at a Starbucks store, the bag was also a coupon good for a free cup of coffee.

When grocery stores ran sales, you could buy a 12-ounce bag of coffee for about $6, and later redeem the empty bag at Starbucks for a cup of coffee worth about two bucks. So, of course I bought my coffee at the grocery store.

Now, Starbucks has changed the packaging, and those free-coffee bags are gone. Instead, no matter where the bagged coffee is sold, it comes with a code that has to be entered online, and you need 10 of them for a free drink at Starbucks. So that's 10 bags of coffee for one free drink instead of one bag for a free coffee.

There's now no incentive to buy Starbucks coffee at the grocery store, unless there's a good sale, but I can go buy it at Barnes & Noble and get a 10 percent discount with my bookstore loyalty card. Not a big deal, moneywise, but every dollar counts.

Companies can change loyalty programs and promotions at any time, so take advantage of them when you can. Hotel points and airline miles tend to become worth less over time, for example, as hotels and airlines change the rules to require more points/miles for the same rewards.

Southwest Airlines and Starwood Hotels, for example, made changes to their loyalty programs earlier this year that made accumulated miles/points generally less valuable. Both offer solid loyalty programs, and I participate in them, but they are less generous this year than last year.

So, take advantage of good deals while they're available, and try not to sit on accumulated rewards, because they may be worth less - or even worthless - in the future.

Reach David Slade at 937-5552 or