I must echo PIF advice, suprise, suprise.

At 9 weeks, your kitty is just a baby kitty! He is prolly playing, and needs another playmate. I swear this isn't just a ploy to get you to adopt another kitty. I have a 9 month old right now that is just so awful...I should have gotten him a playbuddy. My last two were littermates, and weren't anywhere near the trouble this one is.

As to food, unlike humans, where monotony might be uninteresting, remember that kitties might react to new food all the time. I would find one quality dry food, and, it should REALLY be a kitten food at 9 weeks!!!!, and stick with it. Wet food should also be high quality. I only give my guys wet food as a treat. And, it is not very often nor very much.

Good luck!