Introducing food other than milk

When is the earliest? I read something about mushing up rice cereal? My daughter is 2 1/2 months and is becoming increasingly hungry. I breast and bottle feed. With her formula, 4 ounces per sitting would do it but now she wants 6-8 ounces. She gets hunger pains more frequently now and I feel like she's already kind of over the milk only phase.

Just wondering other options to help keep her full... I can already sense her curiosity when I'm eating normal foods.

UPDATE: I was only asking about rice cereal not feeding her 'solids' or chocolate cake lol.... anyway the pediatrician suggested a thicker formula today. Also it's pretty common for moms to give babies rice cereal for acid related problems. Even though we are not.