Well, the tennis racket would make for a crappy weapon (it has no blade, nor does it have enough mass to make a good bludgeon) and it wouldn't last very long anyway.
Out of the things you mentioned, only the dull kitchen knife would be good for a weapon, though you'd have to get in close enough to ram it through a zombie's eye socket or through the base of it's skull to hit the brain (which is harder to do than you'd think - a long, thin metal spike would be better for either option).
I katana would be fine if you could find one that is an actual, functioning weapon and not just a show piece (and most of the ones you'll see for sale are just show pieces). The real deal is expensive though; look to pay a couple of hundred bucks at the minimum. And even with a sharp, full tang katana, cutting off a human head in one blow is rather hard to do despite what you've seen in the movies.
If I were you, I settle for a baseball bat or ax handle made out hickory - either option is relatively cheap and easy to find - and it would also be easier to use either one to cave a zombie's skull in than trying to behead it with a bladed weapon. Also, you could just smash in a knee and they'd go down long enough for you to get away or finish them off.
"Ph'nglui mglw'nafh Cthulhu R'lyeh wgah'nagl fhtagn."