A.,
Are you still breastfeeding? Boost the number of times you nurse (if you're comfortable with it) to make up for the stuff you feel he's not getting. He may be missing the warmth, nestling, and food he's getting when he's breastfeeding.
We started our son off on solids at 6.5 months, but he wasn't interested - we didn't force the issue and just kept breastfeeding more, and getting the cereals in first - they are more important for the iron. Mixed with breastmilk was the only way he'd eat them at that point. He didn't really start cereal daily until 8 months. Jar fruits were what he liked, yellow veggies - and spinach. :) but he would eat only 1/2 jar at age 8 mos. He may be putting in a bid for more nursing - try nursing him just before or after eating.
You might stretch him out to six earlier meals a day - little blips instead of 'big meals' for him. Your son has been eating 12+ times a day for a long time now.
At 9 months, I was still nursing him 10x a day at least, more on teething days. Which reminds me, if he's teething, he'll not be interested in food as much.
Food doesn't help him get to sleep, I've _read_. I don't know that I completely discount food, but I know it's not the end-all be-all for getting sleep. Sometimes it is the baby.
Favorite foods? Don't forget a balance - I have given him veggies for breakfast since day one. :)
He's gaining weight? GREAT! That means one less worry for you.
Don't worry, you're doing great!
Good luck,
M.