I've never found anything a previous owner left behind. The homes I have bought to live in have been completely empty and clean.
However, I have found things that were done by the previous owner that seem a bit weird. This house, there is a bathroom door that opens the wrong way. It opens into the bedroom instead of into the bathroom. In my remodeling, I will be changing that when I get to it. They also covered beautiful terracotta tile floors with wall-to-wall carpeting. I ripped up all the carpet. And one of the sheds out back turned out to be a huge walk-in cooler with wood siding on it. I had that demolished and also a couple of other small sheds removed and built my small barn.