I confess to organizing my groceries on the belt as well, though not by category (but I've never tried intentionally un-categorizing things either). I do try to face the bar codes down, so the cashier doesn't have to twist the products as much (RSI prevention), and I try to pack the belt as tightly as possible so I can get started bagging while the cashier's still scanning.
I think that's "exposure-response prevention"; it's supposed to be highly effective, and researching it' is one of the 170 things in my inbox to do once I process and organize themIf this stuff is really obsessive you could try the behaviour modification technique: look at the torn chair and say out loud `I need to repair that rip'. Count how many times you have to say it until your mind gets bored and wanders onto something else. Repeat that many times as often as needed.