For me, the preferred way to buy comics when I was a kid growing up in the 1970s was off a spinner rack, where you could browse through titles and pick out the individual comics you wanted.
But sometimes, I'd need a comics fix, and the only thing available at a convenience or grocery story were these things: Three comics bundled in a sealed plastic bag. And you could only easily make out what the top comic was.
Sometimes, you could managed to manipulate the comics without damaging the bag and peek at the bottom two comics, but it was always a bit of a gamble.
And that was part of the fun.
Sometimes you'd end up with stuff you just didn't like (or, worse yet, already had). But sometimes you'd get exposed to new titles, writers and artists that you did like.
Though I'm not sure, and didn't have a clue or theory about it when I was a kid, I figure this was a way for the publishers to unload overstock.
Possibly, they chose the "top-featured" comic as a sort of loss leader for lesser-selling titles hidden below.
In any event, I sort of miss them, as I do the entire era when comics were everywhere and nearly every kid read them.
Share your memories, if you got 'em, in the comments below!