Guys you are missing something important here.
Homogenous force fields can't be used to generate energy, only to store it (and get it back when convenient).
In other words even if you can make the cat/bread combination float (or just the bread although I would like to point out obvious handling and maintenance difficulties with entirely buttered bread - it would require magnetic confinement so as to not disturb the butter coating), this would not be sufficient to generate kinetic energy.
There are other examples where the same thing happens, namely superconducting levitation, vacuum-generated attracting force on plates at close proximity due to Casimir effect, gravitational potential energy, springs, and rubber bands.
In all these cases, a force is present, but does not do work. To make the force do work, a deflection from balance state is required - which means you're putting energy into the system.
In other words, no free energy from cats and buttered bread. Both examples would, when dropped, fall to close proximity with the nearest surface in the direction of positive gravitational gradient, at which point the effects of buttered bread and cat would kick in and result in stabilized levitation, at which point it would be of no use to anyone but science fair organizers and the Nobel committee.
There is also a competing hypothesis that the cat would simply ignore the bread and butter, and an entirely buttered bread would simply fall any side down. Also if bread is really light and there's a thick coating of butter, that makes butter side heavier but doesn't significantly move the centre of aerodynamic pressure, and when centre of gravity and centre of pressure are misaligned you end up with a stable projectile that tends to align itself so that centre of pressure is behind the centre of gravity.
Ie. a buttered bread, falling a great distance, would tend to stabilize itself to fall butter-side first.
This view has never gained much foothold, though, and should be considered a marginal possibility only until it has been experimentally confirmed.
By the way, the clever ideas playing around with bread-butter topology are NOT A GOOD IDEA. At best, you'll rip a hole in the bread-butter continuum. At worst, butter and bread crumbs will be everywhere like an Eldritch Abomination.
Also, I have always wondered how buttered breads behave in microgravity, such as onboard a space station. Is the tendency to "fall" butter side down related to gravity, or more of an attractive force between the butter and nearby surfaces, and gravity gradient direction only explains why the bread most often contacts the floor as opposed to walls or the ceiling?
It could be some sort of timeline effect where the adhesive effect of butter acting between surface and bread, from the future, affect the present!
This warrants experimentation.