I think you folks are making it all too complicated. Strapping two cats back to back? Heck, I've bathed our cats, and I think that's too much work.
To make toast float all you have to do it not butter it on either side.
A much more interesting experiment is to butter toast on [i/]both[/i] sides. I'm going to try this one at home tonight. I'm convinced the toast will spontaneously fission when dropped, allowing both buttered sides to land downwards. No radioactive byproducts should be emitted, therefore giving us clean fission!
“Of course,” said my grandfather, stepping from the Time Machine and pulling a gun from his belt, “There’s no paradox if I shoot you!”