In addition to rubber balls, I enjoyed using rubber bathing caps. They were common in the 1950s and 1960s, and almost every woman and girl wore one, but you can still buy them on line even today.
Use relatively plain caps for this technique. I'll explain how to use the really frilly and flowery caps in the next technique. Plain caps will let you feel and manipulate your penis better.
The obvious thing to do with a bathing cap is to place it over your penis and rub away. Once it's lubricated with precum, it's a wondrous experience. It's almost impossible to grab the penis as it slides around. That's not a problem as no matter where it slides, it's rubbing itself against the rubber. Try to coat your entire penis with precum using the cap and try to coat the entire interior of the cap with precum using your penis.
The interior of the cap is important; some of them have a texture. While a cap with a texture can be more interesting than a totally smooth cap, make sure it is not too abrasive. If the cap has a ridge down the middle due to the way it was molded, you might want to sandpaper it away.
When you are done, clean the cap thoroughly and let it dry. If you are going to store the cap for a while, apply a light dusting of talcum powder. Clean off the powder before using the cap again.