Not so fast there, Bobh.

Humans eat food because they require energy to function. The same applies to all other life forms. The machines we build use other means of getting the energy they need to function, but they still have to get it somehow. Eating food because it tastes good works and is useful because most food that tastes good, including junk food, still has nutritional value. You can and do extract energy from it. Fat, in particular, has an extremely high energy density. There are other things you need—atomic elements, as well as molecules your body cannot synthesize—but that doesn't make the other food useless.

You don't have to eat exactly three times a day, either; eating more often or less often is also possible. You could conceivably make an energy drink with everything you need, but you'll still have to drink it more than once a day. Pills, meanwhile, just don't have the volume to fit all the goodies you need, unless you feel like taking dozens of them. Even if you do, this makes you completely dependent on big pharma, which as I'm sure you know is an incredibly bad idea.

Hunger and appetite are there to let you know you're running low. Consider them a fuel gauge, 'cause that's what they are. I'm not sure about cravings, but I'm guessing the idea is to encourage us to eat things that are known to be good.

Pain is a warning light indicating that something is taking damage. Its location and exact feeling can be remarkably informative if you're not too busy being emotional about it. Pain is just a signal; the emotional response to it is where the problems start. That could use some fixing.

Interchangeable parts would be helpful. The human body is not made for ease of maintenance because, until very recently, there was no one around to maintain it. Living bodies have, for the vast majority of the history of life on Earth, had to maintain themselves or die. Surgery is very new. Evolution isn't so quick as to have already caught up with that. Human science is, however, and soon enough we'll likely be growing replacement body parts from stem cells or something.

Sleep also exists for a reason. Seriously. I'm not sure what the reason is, but I'm sure you can imagine that not needing to sleep at all would be a tremendous evolutionary advantage. But it hasn't happened, which would seem to suggest that it's impossible. Even some marine animals that function 24/7 are only able to do so through workarounds like sleeping half their brain at a time.

Automobiles are not superior to humans simply because automobiles do only one thing well—move their cargo at high speeds in relative safety. They cannot maintain themselves, they cannot maintain each other, they're incredibly fragile, they have no brain and a pathetic excuse for a nervous system, they need exactly one kind of fuel or they die, only enormous corporations can produce that fuel in any reasonable quantity, they cannot reproduce and so cannot evolve, and their entire non-species is currently in a state of catastrophic famine. I'll keep my human body, thanks.