Books.
I have always loved reading, but prefer to own, rather than borrow books, so I have a library of thousands of volumes.
However, I don't consider this activity to be a vice, but rather just a pleasure.
I suppose my love of fixing or repairing broken objects or the modification of objects (both photographic and non-photographic) to suit my needs can be construed as being a vice. My wife certainly thinks so, (except when I fix her favorite pairs of reading glasses, which is when it suddenly and magically becomes a skill or talent rather than a vice).