suddenly not eating

My handsome boy is usually the first to scream when it’s time to eat and is good about eating. Last night we noticed that he wasn’t interested in food at all, no matter which type we gave him. We have two foster kittens right now so I thought maybe it’s stress but i’m not sure because they’ve been here weeks and he loves them. The vet is closed today, I can’t afford an emergency vet and I’m not sure what to do in the meantime.

Advice appreciated