I stole office supplies from my job for two years and just quietly returned everything.
For about two years I took stuff from the supply closet at work, pens, notebooks, printer paper, even a few USB drives, way more than I ever needed for personal use. I told myself it was fine because "the company doesn't care," but the truth is I just liked getting free stuff and never gave it a second thought.
Last month, a coworker was written up for "inventory shrinkage" in our department, and it occurred to me that it was probably partly due to what I'd been doing. I felt sick about it. Over the past few weeks I've been slowly buying replacement supplies out of my own pocket and restocking the closet a little at a time so it doesn't look suspicious.
I haven't told anyone what I did, and I don't think I ever will, but I needed to admit it somewhere. It was a small thing that I never thought about seriously until it actually affected someone else, and I regret not thinking about it sooner.