Lots more good ideas fellers, preshate the input. I've put Miss Kim on alert for any practice golf balls and whiffle balls. I figure I'll skip the barbie...but I did laugh my but off on that one..
Forgot to mention the old standby tennis ball, especially the real heavy ones for dogs. I've found those at tractor supply now and then on sale and after the dogs get bored with them I steal em away. Disposable plastic cups make a good sound on impact; and I get to be green...I get some more use out of them after they develop a leak and we can't use them in the house anymore. Ping pong balls seem to crush too easily.
Never thought of the baby powder in the med bottle, bet that makes a heck of a visual confirmation.
On the more bizarre side: I've tried eggs that were too old to use for cooking, and although really cool on impact, they're too messy. We even tried shooting through the hole of a couple of stale donuts in camp one time...course, you only get one shot. We've done apples and pears off the trees but they are a bit messy too. Potatoes work ok if big enough...but don't ask me about tomatoes
Any other suggestions?