I have not had a lot of success with toys but the ones others have reported and the items I have used that got the octos attention all floated. In SueNami's case, a floating plastic ice cube with a plastic zip tie and food at the end of the zip tie got more attention than any other item. The other toy we concocted, taken from something another member had success with, was a couple of straws tied together in the center. I would put Beldar's feeding stick in one end and she seemed to enjoy riding around on the contraption while dining.
Carol has had several of her octos play with a large lego block. Two of them learned to ride it.
I don't remember anyone else trying a test tube but I did try a multi-shot shot glass a few times (the crab kept escaping in spite of the thin neck dividing the shot sections).
The "feeding sticks" a lot of us are referring to come in two varieties. The heavily used bamboo feeding stick is found in packs of 100 at the grocery store under the name bamboo skewer IMO this is the most used (for lots of unexpected things in addition to feeding) and preferred. There is also a thin acrylic rod with angled tip style that is found in a fish store marked feeding stick
i gave mine a few transformers. one of them it disassembled at every joint and i found it scattered across the tank the next day. another one it ignored, and another one it very excitedly caught before it hit the bottom of the tank and pulled it apart. it showed some, though less interest when i put it back together and dropped it in again. another one is consistantly ignored. it reached out and took a hold of it, looked for a few seconds and then put it back in my hand.
all the moving parts and joints seemed to give it alot to play around with, just get one with alot of ball joints so you can pop everything back in place and let it start all over again. i have a few pictures of it with one if you type 'octopus prime' in deviant art.