We're very spoiled in modern Western civilization. Despite the very real numbers of underfed people in the US and other first-world nations, the large majority of people in these countries have never truly gone hungry. If we miss one meal we say that we're "starving" and lament on how hungry we are. Most of us (myself included) don't know what it's like to actually starve and have rarely missed a meal. This kind of attitude also carries over to our pets, where many (if not most) clients seem to think that if their dog or cat misses a single feeding then they're quickly on the way to death.
The average person or pet can go for days without eating and have no significant adverse effects. I have personally done a 10-day fast of only liquids and personally know someone who has done a 40-day liquid-only fast. Though you have to do extended fasts carefully in order to remain healthy, it certainly can be done. The same is true of dogs and cats.
The reason for bringing this up is what happens when people see their pet miss a meal. The scenario is all too common....a dog or cat misses one feeding, often for less than 24 hours and the owner panics. Suddenly they worry that their pet will starve to death and scramble to get them to eat "anything". They may offer ham, hot dogs, steak, hamburger, cottage cheese, rice, bread, and many other things, usually food items that we recommend never to feed. It can be really frustrating to vets as these things can cause or compound disorders besides whatever caused a decrease in appetite in the first place.
So let's be clear here. If your pet hasn't eaten in a few days, please don't try to feed them whatever you have available in a desperate attempt to get nutrition in them. Unless they are severely underweight already, are very young, or of a species that needs to eat frequently (such as some rodent species), they won't starve to death in a couple of days. Even breeds of dogs that may have a tendency for hypoglycemia are usually going to be fine. Now, if there is some underlying medical condition such as diabetes you certainly want them eating regularly. But that is the time to see your vet, not try random foods. Many human foods can cause digestive upset, pancreatitis, blood sugar imbalances, and even potential toxicities. If the pet is just being picky, by giving in to them and feeding human food you are actually encouraging and reinforcing such behavior. Don't do it!
There are reasons why pets will decrease or stop eating. It might be pickiness or it might be a serious illness. Regardless of the cause the answer is never "feed anything". Talk to your vet, get to the root of the problem, and then choose appropriate and healthy measures to correct the issue.