I know what you mean.. I had this plastic tricycle thing that I used to ride around on when I was maybe 7 or 8 and I discovered that riding over a particular bit of bumpy ground gave me a very enjoyable sensation in my pants and I'd do it over and over again. From around the same age I used to fantasise about wetting myself and being leaned over the side of the bath and spanked, being gunged ('slimed' in America I think?) or being made to dress up as a girl in front of my friends, they all gave me the same pleasurable feeling. It was all humiliation based stuff and they all turned into sexual interests later.When I was young, I also had some what I guess you'd call non-sexual masochistic interests. There were certain fantasies that I enjoyed thinking about. (Maybe it was what would become a sexual interest, and I was just too young for it to manifest that way.) I'd imagine turning into a Pokemon and being kept in a cage by my family, for instance. (There was an episode of Pokemon where Ash is turned into a Pikachu, which gave me a very "deep" feeling.) Or permanently losing the use of my legs. Over time, that interest became sexual and focused on diapers and age regression.
I used to do exactly the same thing with plastic bags as a young teenager. Eventually I gave up because it never worked properly and moved on to an old pair of speedos I would wash when my parents were out of the house.Other times I used plastic bags. I'd cut the handles off. Then I'd cut the corners off to make leg holes, which stretched to fit of course. Then I'd put a lot of paper towels in them. I've never heard of anyone else making anything like this; I guess they aren't too bad for simulating plastic disposables. I'd mess them and then spend a very long time cleaning up.