One creative idea is to make the stories about baby's future dreams. For a Twix bar, you could create a story that the baby will have two big dreams in life, just like the two sticks of Twix. Also, you can create stories around baby's first words. If it's a M&M's, the story could be that the baby's first words will be as colorful and fun as the different colors of M&M's. You can also use different baby products in the stories, like for a Baby Ruth, you could say that the baby will be as strong as the baseball player it was named after and will need a lot of baby powder to keep clean.
You can base the stories on baby animals. For example, if you have a Reese's Peanut Butter Cup, you could say that just like the peanut butter and chocolate combination, the baby will be a unique mix of two things, like a little bunny that's both fast and cuddly. Another idea is to use nursery rhymes in the stories. For a Hershey's Kiss, say that the baby will be as sweet as a kiss in the nursery rhyme 'Twinkle, Twinkle Little Star'.
Some creative ideas include making the stories time -based. For a 3 Musketeers bar, say that the baby will have three important times in its life - birth, first birthday, and first step. Or you could use baby's emotions. For a Skittles pack, say that the baby will have a rainbow of emotions just like the different colors of Skittles. You could also make the stories about family members. For a Butterfinger bar, say that the baby will be as tough as a family member who is always there to protect, and at the same time as sweet as the Butterfinger itself.