Most times I thoroughly enjoy making a mess when I ejaculate, even in open adult theatre situations. However, there are other times when I want to be able to masturbate to ejaculation, but I want to avoid a mess.
Toward this end I use a non-lubricated condom. After I'm erect, I leave a 1'-2' sack at the tip of my penis to hold my semen, and then I roll the condom-roll down over my helmet ONLY. I leave the condom-roll at the bottom of my helmet, rather than rolling it all the way down to the base of my penis. With the condom in place in this manner, I can masturbate freely with my hands directly on my bare-back penis, and then when I ejaculate, my semen will squirt into the 1'-2' sack for easy disposal. This is great for masturbating on trains and planes, and anywhere else a mess should be avoided.