The details of plastic bagdom are ever in flux. Cities are trying to ban them. Stores are giving people money to not use them.

Today, a major national pharmacy retailer joined the fray. CVS announced what is basically a 25-cent giveback for every bag a customer doesn’t use. Great deal, right? Especially when you consider that most grocery stores only give in the neighborhood of a nickel.

But there’s a catch. You need one of those horrid little cards — “loyalty” cards is what they’re often called — to take advantage of the deal. Actually, you need TWO of those horrid little cards.

Do I need to say here how much I hate all those horrid little cards and tags that we’re supposed to carry around on our key chains to get a discount at some store or other? Am I alone?

I have cards at two grocery stores. For a while, I had a card that gave me a free cup of coffee every tenth time. My pet food store gives me some kind of cut if I use their card. And so on. If I took advantage of all of the cards and deals, I’d just about need an extra purse.

So, yes, I rolled my eyes when I heard about yet another discount card, even though CVS promises theirs — a “GreenBagTag” in the shape of a green leaf — is made with corn-based material and 100 percent recycled silicone.

Except that the 25 cents really is a good deal, so bear with CVS in figuring out how it works. I've distilled it into ten easy steps:

1) Sign up for an “ExtraCare” card, which is free and entitles you to various discounts. You cannot get a GreenBagTag without it.

2) Hand over 99 cents.

3) The clerk will give you the tag. 

4) The GreenBagTag comes in a little package — it’s made of recycled paper, but still, go figure. Please save this so you can recycle it.

5) Next time you buy something and don’t use a bag, swipe the ExtraCare card AND the leaf-shaped tag.

6) Do it again.

7) Do it again.

8) Do it one more time. Only after the fourth bag denied does the computer tally a $1 discount, which CVS calls the “Extra Buck.” It’s printed on your receipt. Your paper receipt.

9) And now ... don’t lose that receipt! May I suggest paper-clipping it to your leaf card, just in case your key ring isn’t already bursting?

10) Next time you’re back in any of the 7,000 CVS stores in the nation, hand the receipt to the clerk, who will scan it to give you the ExtraBuck credit on your purchase.

Got it? Stay tuned for the tally on how many plastic bags this saves.