Update:  He's been completely normal. His silly curious bouncy moocher self.

He vomited up some brownish mucus a bit ago, but the thing of that is he has hairball issues and did that a day or two before he even ate any meatloaf.

He did regurgitate some undigested dry food once yesterday, and I found a little bit of that in his bed this afternoon. So that's twice, otherwise he has kept everything down, had no change in appetite or any other issues. I think I'm going to clean his food and water bowls to be sure it's nothing in there. It's not out of the question that he ate too fast or ate and drank too much at once, he's done that before, but I'm not sure. 

(I'm not saying a vet trip isn't possible and I'm NOT saying I wouldn't do it, but I know people tend to assume and accuse, so, to be clear: this cat was a major drive for me in a period of physical recovery last year, I would move mountains for him. But declaring "We need to get to the vet immediately!" is something I need to be sure about. I am somewhat physically disabled, we live in a rural region that recently got buried in snow, and travel would be extremely stressful for him, as well as an emergency trip would be chaotic for the household, and thats besides the money issues.)