1988 - Marvel Superheroes Secret Wars Sticker Album

By Panini.

1985 - Dorman's Cheese Secret Wars Puffy Stickers

In partnership with Dorman Cheese.

Here's the Marvel Comics ad.

It looks like they re-purposed these puffy  stickers.

To create these Marvel Super Heroes Secret Wars Puffy Stickers.

And here's the Sticker Album.

1983 - Marvel Comics Super Heroes stickers

I remember having these stickers as a kid, but can't recall how I got them. I've seen a few eBay auctions selling individual sheets, but not sure if they were part of an activity book or stand-alone stickers...