I think the question is quite well summed up in the title but I will just clarify that by preparing food I am including ‘mashing together’ ingredients or even something as simple as having different types of food in each hand and alternating bites to form a mixture in the mouth. Cooking food could refer to something as basic as leaving food out in the sun to heat it up. Basically I am wondering if there are any animals that take steps to improve the taste of food beyond how it naturally occurs.
There is a group of macaques that wash potatoes give them by researchers. It’s thoguht that they wash them to get the dirt off, but it might also be to make them a bit salty since the washing is done in sea water.
I seem to recall that certain ants seemed to store thier haul in such a way as to encourage it to ferment and that they did’t seem to eat it until it was ripe. I’ll have to look for a cite on that one to be 100% certain. Get back to ya.
This is probably not by definition a “preparation”, but it’s common for housecats to play with their food before it’s fit to eat.
Anything from picking it up and dropping it outside of the bowl, to pushing it around the fllor first, as if they’re hunting it before they eat it.
Many birds feed their young by first eating something and then regurgitating it into the chicks’ mouths. I’m not sure how much “pre-digestion” happens there, but I imagine the food is at least softened up a bit.
I wonder if the ruminating done by cows qualifies for what you’ve specified.
The Leaf Cutter Ant not only prepares his food, he also a farmer! Must be some mighty tasty fungus.
I remember my dad telling me that Racoons wash some of their food before they eat it (maybe it was just fish). But I can’t say I’ve ever seen an episode of Nature back up that claim.
I’ve also heard that if you give a racoon a sugarcube that they’ll wash and wash it until it dissolves entirely. That might be an urban legend though. Doesn’t say much for the intelligence of racoons.
My biology-studying friends tell me this is because doing so would logically scare the bejeebus out of the critter about to be eaten, and that adrenaline apparantly tenderizes the meat or tastes good or something.
I have a friend who’s something of a redneck, and he says he gives Racoons sugar cubes because of that amusing bit of behavior. Then again, he also claims that he and his brother, in a jeep that had no brakes, no radio, a sofa tied down for a seat, and a diver’s lamp for headlights, were chased by a very large, very angry mountain lion down a mountain road, so I dunno how much to believe most of what he tells me. 
I’ve heard suggestions that part of the reasons wild dogs bury pieces of meat is because they like the flavor it acquires when it starts to decay.
My youngest dog uses her nose to splash water over her food, then waits until it gets soft. Dunno if that improves the flavor, but she seems to like the texture better. (And no, concerned Dopers, she has no teeth problems. Even the vet said it must just be preference.)
All sorts of creatures are known to smash nuts, if that counts, and I’ve seen elephants at the zoo step on a watermelon to smash it open before consuming it.
Alligators stash their prey underwater for a few days or weeks to allow their kills to decay somewhat and soften up before consuming them.
Spiders inject prey with a paralyzing toxin. Keeps them alive with the autonomic nervous system running but motor shut down. Like Michelle Pfeiffer in What Lies Beneath. The spider wraps up the prey and hangs it until it’s ripe enough to suck the juice out. Remember incidents of this in both The Hobbit and The Lord of the Rings? Tolkien must have had a “thing” about spiders. His earliest memory was of being bitten by a tarantula when he was 3.
I was also going to post about alligators letting dinner ripen. How about using tools to reach the food? Some animals, chimps for sure, use sticks to get ants and termites out of their holes.
I wonder about shrikes? They impale dinner on thorntrees and let it sit awhile too.
Oh, and other animals besides birds regurgitate for their young. I know wolves certainly do it.
Adrenaline makes meat taste tough and gamey. Modern abbatoirs go to great lengths to keep the cows calm right up until the moment of death for precisely this reason.
That’s only an issue if the meat is going to be stored long enough for rigor to set in. Stress depletes the muscle’s energy stores leading to acid buildup during rigor contractions, hence the gamey taste and stringy texture. Of course cats eat their food well before that so it isn’t an issue.
Having siad that, the idea that cats play with their food to improve the flavour seems highly unlikely. Given that cats live on a natural diet inlcuding cockroaches, carrion and injured mammals and birds I doubt very much if flavour enters into it.
What about frying squirrels?
I’m sure I saw a documentary where some kind of animal puts their food into a thermal vent or something to cook it before eating.
I can’t recall any more detail than that, not even what animal it was, so really that’s probably not much help and likely to be inaccurate anyway.
Don’t female bears make porridge?
I can’t believe I’m the first to mention bees! It’s quite a process to make honey. They not only make it, they carefully dehydrate it and store it. See here.