Here's a (bad) photo of the inside of the card. I put in a recent picture of my husband with my sons and the phrase "our pop rocks" with the Pop Rocks candy.
I started by measuring the Pop Rocks packages and built the card around that. I cut a strip of black cardstock that was 6x12 and trimmed it to 6x9. I scored it at 4" and 5" to make the 1-inch thick "spine" for the card. I used the extra 6x3 piece of black that I cut off in the previous step to make a little sleeve for the Pop Rocks. Then I embellished with the Superhero papers and some messages printed from my computer. (Download the font "Masked Marvel" from dafont.com for free.)