Most B&Bs offer some kind of hand soap, body soap, shampoo and such. We also have shower caps (which are much more popular in the winter), hair dryers, and sewing kits. Facial tissues and an extra roll of TP are pretty standard too. I like to put the items on a pressed glass tray or bowl of some kind as they are dressy, inexpensive and very easy to keep clean.
By far, our most popular bathroom amenity is a stash of Q-tips! We offer them in modified sugar shakers to help keep them clean and to discourage people from mindlessly putting a dirty one back in with the clean. (Just pull out the metal shaker part from the top of the container.)
Our second most popular bath amenity is a magnified mirror. One of our frequent guests moaned about forgetting her traveling mirror. A gentleman said that he had trouble seeing the mirror when he shaved. The two comments in one week prompted us to install the mirrors in all of the bathrooms. (This is why we love to hear how we can make the place better. Seely doesn't wear make up and Dave has a beard so it would never have occurred to us that guests would like magnifying mirrors.)
Those are the things that Works for me Wednesdays (and the rest of the week) around here.