So, this comes out of me being a bit of a terrible cat parent. I forgot to pick up more wet cat food, and we are now out. Due to various constraints, it will likely be Friday afternoon before I can easily go get more.
Now, I'd really hate to deprive my cat of his morning breakfast for that long, because I know it is good for him and he loves it.
Is there anything I can prepare at home that would be similar to what he gets, assuming just an average can of wet can food?
There are really two concerns here.
Safety
The danger in meal replacements is the loss of taurine that is added to commercial cat food that cats need to survive. According to VCA Animal Hospitals:
Taurine is exclusively found in animal-based proteins. It is critical for normal vision, normal digestion, normal heart muscle function, to maintain normal pregnancy and fetal development, and to maintain a healthy immune system. Most mammals are able to manufacture enough taurine from other amino acids to meet their needs. However, cats have a limited ability to manufacture taurine; therefore taurine is classified as an essential nutrient in the cat. Fortunately for the cat, taurine is readily obtained from the diet, as long as the diet contains animal-based proteins. Unfortunately, it is not stored in large quantities in the body and so must be consumed on a regular basis.
Clinical signs of taurine deficiency are slow to develop. It can take between five months and two years before symptoms become apparent, depending on the cat's life stage.
If taurine levels are deficient, the retinal cells of the eyes will eventually degenerate, impairing the vision. This condition is referred to as feline central retinal degeneration (CRD). Deficiency of taurine will also lead to a weakening of the muscle cells in the heart, causing a condition called dilated cardiomyopathy. Taurine is a component of bile salts, and its deficiency may cause digestive disturbances.
(VCA owns/runs many of the emergency and specialist veterinarian hospitals in my area. I've been to 2 of their facilities and found them extremely competent).
For a few days a reduced supplement concentration (you're still feeding dry, just one meal is supplement-free) should be fine. If you were doing shift work or something and couldn't get to a pet store for longer than that, I would suggest looking into Amazon or other delivery options in your area.
After considering the safety from missing Taurine, I would also consider the potential dangers of the candidate materials. The most important ingredient is a meat source.
In the US, boiled chicken (no spices) and rice is often recommended by veterinarians for cats who have stomach upset. I would consider that safe.
Many people will give their cats cans of tuna, but that may not safe depending on your level of risk tolerance.
Beef (perhaps as of hamburger) is also common in US households, but if your cat does not already eat beef foods I would not recommend it (I've seen anaphylaxis in cats unaccustomed to beef before).
Palatability
I suspect that this will be the real problem in suddenly changing your cat's food. I have never been able to get a cat to eat chicken and rice (even when they're feeling good, as an experiment to see if they didn't eat it before because they felt bad, or because they didn't like it).
There are pages and pages of strategies written on the web for how to switch your cat to raw/homemade food just because most cats (especially dry food fed cats) don't recognize it as food initially.
You can prepare the most healthy replacement, but if he doesn't think it's food, he won't eat it.
What I suspect the best strategy will be to think about any time he's shown interest in something that you've eaten (climbed in your lap, licked a dirty bowl, etc) and if that's something that's reasonable, make something like that.
For example, I had a cat who once showed interest in chicken wings. Boiled chicken with just a TINY dab of BBQ sauce (for smell/interest) might have worked on him. I had another cat who wanted string cheese. That's not a reasonable food.
If your cat has never shown interest in human food (or only inappropriate foods), just give him dry food for a few days and get to the store as quickly as you can.
If this is a recurrent problem, many pet food suppliers let you set up delivery subscriptions for pet foods so you won't forget (I do this! I recommend it!).
Below is my list of emergency meals for cats made from people-food in order of preference:
Boiled chicken and rice is great for a meal or two.
Scrambled or hard-boiled eggs with no seasoning, cooking oil or sprays.
Other cooked meats like fish, turkey, lean beef or pork.
Low-fat deli meats.
Canned tuna will work in an emergency as well, but the mercury present in tuna is best avoided.
..and lastly it should be mentioned cats will eat some veggies. While a cat can't live on vegetables, in an emergency situation feeding a cat some veggies is better than letting it starve. Peas, carrots, spinach, cabbage, kale, squash, sweet potatoes, corn, broccoli and asparagus are all cat-digestible. One of my cats will go to great lengths to steal and eat some spinach or broccoli.
Just to make it clear, even the best of the above, chicken and rice, is not a balanced meal for long-term feeding. Cats also require the B-complex vitamins, vitamin E, taurine, fiber, omega 3's, calcium (bone meal), phosphorus, other minerals, and a bit of the vegetables mentioned above.
I have used human tuna fish cans when I have forgotten cat food for a day or so. Boiled chicken is also good.
True cat food has additives that a cat needs for health, so you don't want to make this a permanent change but a few days won't hurt.
As a reminder: There are many cats who have lived long and happy lives on dry food. Missing a few days of his wet food treat may disappoint him, but nothing worse than that.
My kids are currently getting as much dry food as they want, and about 1.5 oz (half a small can) of wet food roughly every other day, with some deliberate randomization of which days and at what time so they understand it as a treat and don't pester me for it. Even as a treat, and with this small amount, they often don't finish it. (They're most interested in the "with gravy" versions, and will try to get all the gravy before they consider whether they'd rather eat the chunks or go back to their dry food.)
It's worth knowing what else is safe for them to eat for a few days, but I really don't think you're being "a bad parent" if they have to settle briefly for dried. Stop beating yourself up about it; it's no worse than telling a picky human kid that you're out of green beans and they're going to have to settle for other veggies for a day or two.
(It's sometimes surprising what cats will nibble on. One of mine used to like broccoli; certainly not a complete diet, but cats will eat some veggies so it isn't totally surprising. Another decided that graham crackers and cheerios were interesting; I guess the texture isn't that different from kitty kibble. Then there's the one who insists on eating bits of fluff and string if allowed to do so (bootlaces seem to be thick enough not to provoke that reaction), the one who insisted on licking plastic bags (we accused him of having a "long-chain hydrocarbon deficiency"), and the amazing self-propelled automatic paper punch ("I'm not kidding, the cat DID eat my homework -- or at least shredded it.") Weird little critters. It's one of the things we love about them.)
When I run out of wet food I take a bit of dry food and add water or a bit of the juice from a tuna can or salmon(they like that better) mix it up. Sweet potatoes are safe to give cats as is rice, true they don't absorb much nutrition from it but it is needed for the fiber(Don't give white rice). Another good item to give them is giblets. I will just boil them in a bit of water and through in my mini food processor to mix it up so it looks like wet food...most don't have those laying around but I will pick some up on occasion when they are on sale and keep them in the freezer to use as a treat or if I need it for a few days before I can get back to the store.
