Just One Club Card makes a card, double-sided, with barcodes for up to eight different stores.
Type in the barcode number for each of the cards you now have, then choose its store. If it's for a store not listed (they have 200-plus), e-mail the site owner to get it added, but don't ask about Blockbuster since their barcode is also your account number. As the developer notes, "best not to be shooting those around the Internet." In other words, he takes security seriously.
Click Create your card to see, review, print, cut, fold, and stick in your wallet. Less wallet clutter is good.