The following are Very Important Items, at least for the ones I list on eBay.
Scotch tape. I spend a lot of time taping up dust jackets for books and repairing sewing pattern packets.
Glue. Mainly used to repair the spines on books. Certainly not a sanctioned book rehabilitator, but it works.
Goo Gone. Removes sticky, gummy, gooey problems (not a paid promotion). Sometimes labels will not become unstuck and there is yuck all over otherwise good CD cases.
Vogue sewing patterns are my best selling and I delight when I find them in the thrift shop wild. Here is a recent listing.