In 1975 7-11 gave out the first?

Question

In 1975 7-11 gave out the first collector Slurpee cup what was the first collector based on?

Answer 1

I'm confused...

To capitalize on the popularity of the Slurpee beverage, 7-Eleven began introducing Slurpee collectors cups in 1972.

There are four major sets of Slurpee Comics cups: a 1973 DC comics set, two 1975 Marvel comics sets, and a 1977 Marvel comics set.

http://www.myslurpeecup.com/

Answer 2

Marvel series with Tropic Comics characters.

Red Sonja was first up.