The 1980's, the Era Of Marvel Promotional Comics
There are many Marvel promotional comics, in fact Marvel had a division devoted to them for a time, but the main era that promotional comics really came into their own and Marvel had a lot of them come out was the 1980's. Marvel has packaged comics in newspapers, catalogs, magazines, menus, toilet paper … though that last one was just a product of the 1970's. During the 1970's Marvel really experimented with promotional comics, but by the 1980's Marvel had it down, and we see an expansion of comics into bubble gum. Now comics printed on the wrappers of bubble gum pieces isn't a new promotional tactic, it's Bazooka Joe's whole thing, and even Archie had gotten in on it in the 1950's. However, Marvel teamed up with Amurol Products to create a series of four comics called the Bubble Funnies Miniature Comic Book Collection, and the first entry was, of course, Marvel's favorite son Spider-Man.
Obscure Comics: The Amazing Spider-Man Bubble Funnies #1: In The Clutches of Doc Ock
The Bubble Funnies Comic Line
Marvel produced four of the Bubble Funnies comics, released shrink wrapped with the comic having a piece of gum tucked in the back cover (look carefully at the scans for the cover and back cover and you'll see the gum sticking out the top and bottom). All four comics were full cover, featured ten pages and measured 2 and 5/8 inches by 3 and 1/2 inches. The line was all published in 1981 and made available in July.
The comic did have a variant, with the back cover either having the ingredients list in white, with the UPC, or in blue, above the UPC. (A very minor difference and neither is more rare.) The line only had four issues with Marvel, before Archie took over the numbering and did a 5th and 6th issue with their own characters. The comics can be found in several places ranging from $12 for a near mint copy to $5 for just a readable copy, or even $15 to $20 for a set of all six, just have to browse. The comics have no official online presence, but this comic is a fun read to hunt for, just don't spend a lot on this very short tale.