Don't rule out reflux, especially if he throws up or spits up lots. My ds had severe reflux from birth to 6 months (on the first medication he was still throwing up 15x a day), and he always slept flat on his back very comfortable and a car seat made no difference to him. Not all meds work the same, we had to switch to a 2nd before it helped ds.
As for the foods he's eating, that's a pretty simple diet with mostly nonirritating foods. I have read that some babies find rice cereal hard on their tummies, my ds wasn't fond, it didn't sit well with him so he only has oatmeal or barley cereal, and I would totally eliminate the bananas. I've also read that papaya is harder on their tummies but I find it odd because I've read that papaya's enzymes aid digestion, but maybe try to eliminate it to see if it makes a difference anyways.
((Hugs)) for your dd, I felt bad for my dd as I had to fuss so much with my ds in the beginning with all of his throwing up issues, I always felt the poor thing was just sitting and waiting for me to finish so she could play with me. I think it's a smart idea to start a food diary, it would really help you figure out what is at the cause of his gassiness.