I did this once; somewhere on my phone I have some crappy photos of the results. I used a few materials with differing results.
The thin water bottles worked really well; they did a good job of showing when a cut penetrated and how far it went by the flow of water. The plastic on these (I used the .5l ones) is really good for testing things like edge alignment, but not so much for the penetration of a realistic target, since the plastic is pretty thin.
I believe I also used an old milk bottle, but I'm not sure now....it's been a while.
I also tried one of those apple juice bottles, but with no luck whatsoever. Those things are way too tough to penetrate, at least without nailing them to a surface first (mine were sitting on top of a trash can in extremely ghetto style. That
is how I roll, after all.

)
Bananas were a good choice, because the thick skin offered some resistance, and apples gave me nice clean slices. I didn't try any meat, mainly because I didn't have any on hand.
One thing to be careful of here is something I dodged a bullet on. If you're test thrusting, don't use anything too resistant unless you have a decent handguard on your blade to stop your fingers from sliding up. The ghettocity of my set-up saved me the problem, because the resistant materials bounced off the tip of the blade rather than drive the handle backwards. But if I'd nailed that apple juice bottle down to something, it might have fought back.
I'll see if I can find those photos.
Jason
I'm impatient with stupidity. My people have learned to live without it.--The Day the Earth Stood Still