I’ve always interpreted “have” as retain. It’s either sitting there on your fancy, crystal cake plate or it’s gone because you’ve eaten it(sitting in your cake hole, if you will). In other words, you can’t have it both ways. So either version would be correct.
I left that option out on purpose because I want to know what the idiom is that people say. I agree that it makes sense either way, but I only *say *it as have/eat.
Sorry’ bout that; I’ve never heard it any other way but have/eat.
You can’t haz your cake and nom it too.
I’ve always heard that the phrase refers to fancily decorated cakes (like elaborate wedding cakes), and “have” means to admire it and/or show it off. At the very least, this should illustrate motivation to possess cake without eating it. You have to choose between saying “Hey everyone, check out this amazing cake! Isn’t this the swankiest wedding reception ever?” and saying “Hey everyone, let’s all eat some cake!”.
Anyone hear the title of this thread in Gene Rayburn’s voice? Or is that just me?
You can’t patty your cake and bake it too.
Yep. You can either have a cake in your possession (to look at etc) or eat it, not both at the same time.
Eat/have is the only way that really makes sense as a modern English sentence.
Nevertheless, have/eat is the way the idiom is actually said. Since when do idioms have to make any sense?
You never saw that *Seinfeld *episode about the slice of wedding cake from the Duke & Duchess of Windsor?
This.
We’ve had this thread before and that tends to be the consensus. The idiom is just phrased poorly. It’s pretty old, anyway. I propose we scrap it and substitute it with:
You can’t use your cellphone’s vibrating feature to masturbate and talk on it too. Unless you have a Bluetooth.
Eat, then have. If you say “You can’t have your cake and eat it, too,” you’ve loused up the meaning. As Leo Rosten said, that’s like saying “Out one ear and in the other.” See, if you’ve eaten the cake, you can’t have it, because you’ve eaten it.
Language evolves of course, and normally I don’t mind, but in this case, it bugs the holy shit out of me.
It’s not an all or nothing deal. You can eat some and have some left too. The saying never says the whole cake, and what kind of pig eats a whole cake in one sitting.
That’s awesome.
or
Cake frazes rulz.
Have and not have.
Unless it’s in a box with a cat, in which case the cat’s probably eaten it anyway.
In that case the saying would be “You can halve your cake and eat it, too”. 
You can’t tell people to eat cake and keep your head too.
Well, that’s not what you asked. You asked what people are supposed to say so I chose option 2. If you asked what people actually say, I’d have chosen option 1.
“Have and eat.” I’ve never heard it the other way around. I’ve read the reverse in a book on linguisitics or perhaps just English idioms in general as a more logicial reworking of the idiom, but I’ve never actually heard anyone say that.
Sorry to nitpick but it’s
“If you don’t eat your meat how can you have any pudding?”
or
“How can you have any pudding if you don’t eat your meat?”