Having a key chain full of plastic rewards cards doesn’t necessarily mean you’re getting the best deals. These tips from Parents magazine help gage when signing up for a membership program is worth the cost and when it’s not.

Roadside assistance: If you need your car towed or tire changed even once during the year, an annual membership in a club like AAA can pay for itself, says Joanne Helperin, an editor for Edmunds.com car guide. An added bonus: Members are often eligible for discounts on everything from train travel to prescription drugs.

Store rewards: The 10 percent discount that comes with that $25 bookstore rewards card might sound great, but it will only pay for itself if you buy $250 worth of books. Before you give in, figure out whether you shop at the store enough to benefit from signing up.

Warehouse club: You can more than make up for your membership fee if you buy electronics or appliances, says Teri Gault, CEO and founder of thegrocery-game.com. Groceries tend to be cheaper too, especially if you buy them in bulk. But watch out: There are so many good deals that it’s really easy to leave with more than you want or need.

Attractions: If you visit the local theme park, zoo or museum more than two or three times a year, signing up is almost always worthwhile, explains Robert Niles, editor of themeparkinsider.com. Discounts on food, merchandise, and parking make membership an even better deal.