I feed kibble, but also plain Greek yogurt (not sugar or flavor), coconut oil (just starting this, very slowly), sardines (he goes crazy for these), homemade liver treats made with potato flakes and other grain-free homemade dog treats. I freeze plain pumpkin and yogurt in a small ice cube tray and he gets that every once in a while. I do feed the yogurt every day, though.
I plan to try boiled chicken and I have some lean leftover ground beef and ground pork that I think I'll cook up and try after draining as much fat as possible. I'll only give this in small amounts, though. I try to give him variety, but only a little at a time to avoid upset stomach.
ETA: Our guy is thin, as we just rescued him, so I haven't been decreasing his kibble to add these things. He's putting on weight now, though, so soon I will have to decrease his kibble when feeding the extras for obvious reasons.