If you are doing a century and don't plan on finishing within the top people who may be trying to race the 100 miles you can eat whatever foods you want as long as you don't get sick. The advantage of bars and gels is that they digest faster so if you are in a race you can accelerate without your food kicking you in the stomach for overdoing it.

You can eat whatever foods you can tolerate and if you plan on doing a century I would highly suggest bringing food that are tried and true. Meaning only bring foods on your ride you have previously tried and felt good using. I prefer bananas, cottage cheese, and diluted juices such as apple or cranberry. Don't bring any juice that is very low glycemic. Orange juice is the worst on ones stomach.