Just great artwork.
The backs form a game board.
One card has the game directions on the reverse:
There are 12 'Pop Out' cards which feature the major characters:
Here is a look at the backs of these:
The 'completist in me appreciated the fact that Topn included the Eskimo Pie coupon that was inserted in each pack!
Poking about on non-sports sites told me there was a 'promo' card. I found one on eBay for a buck or two. It is pretty much a dupe of the Batman pop-up card on the front. Here they are together with the promo card on the left, regular card on the right:
The backs with the promo card announcing the sets release date, etc.
Tom, I really appreciate your generosity. This is a nice addition to my modern Batman collection. I have a few things set aside for you and once they holiday nuttiness quiets down I'll be packaging them up for you.