I've been eating Quaker Chewy Granola Bars forever. S'mores is my favorite flavor (I never understood why someone would go with plain chocolate when you could have plain chocolate + marshmallows), with Oatmeal Raisin a close second. They're pretty aggressively sweet, which I loved as a tween and still love now, and they have an awesome bendy, chewy texture that Nature Valley took way too long to catch onto.
Anyone who's tried to make granola bars at home knows that the chewiness is the most difficult part to replicate. I think it comes down to two factors, the first of which is a little corn syrup. But no! What about honey? Agave? Stevia syrup? Not going to work, I say (feel free to prove me wrong), and really, granola bars are pseudo breakfast candy so a little corn syrup isn't out of line. I do add honey, as well, to impart flavor.
The second key to these bars is using quick cooking oats (I generally use the thickest rolled oats possible for other oat-based recipes, like cookies). These oats absorb liquid easily and meld into a coherent texture, creating the desired chew.
As for the add-ins, I decided to go whole hog. I was in the mood for trail mix, which is often a random assortment of whatever's left in my pantry from other baking projects. This time, that included everything from cranberries to coconut flakes to peanut butter chips. Feel free to play around—dates, peanuts, and chocolate chips are just a few other options that would be most welcome.