I have OCD.
My biggest thing is even numbers. I have to do everything in an even number: eating, studying, running, shopping. I also have very specific eating rituals, how I chew and so on and so forth. I also have the obvious problems with germs, and needing to check that doors are locked/that I have my keys and phone, so on and so forth. I am better than I used to be: I can now step on cracks in the pavement and stuff.