Sadly, MK counter service is the worst of the four parks. We've never eaten breakfast there, but I've heard good things about the cinnamon roll at Gaston's Tavern and as others have mentioned the waffle sandwiches at Sleepy Hollow get a lot of good reviews.
As for lunch, we still like Pecos Bill but it's not as good as before the shutdown - no fixin's bar hurts. We used to like Columbia Harbor House, but haven't been in a while. I know the menu has been pared down from before. Honestly, for lunch I'd hop on the monorail and take a break from the crowds and heat to grab something at one of the hotels. Captain Cooks is great (pulled pork nachos are delicious!) and I've heard good things about Gasparilla Island Grill. Or even take the boat over to Wilderness Lodge and go to Geyser Point. It's rarely busy during lunchtime and that food will beat anything in the MK by a mile.
For snacks you can't go wrong with a Dole Whip. I especially love the floats and the tropical serenade. I'm probably the only person on the planet that doesn't like the spring rolls though

. I found them way to greasy and just not that great, though they are very popular.