In my case, this turns out to be insect repellant.
Obviously, what happened is that I took several trips where I needed insect repellant and either didn't remember I had any or forgot to pack it. The latter definitely accounts for one of the bottles, since it's Australian insect repellant and I suppose I bought it in Brisbane on the way to Papua New Guinea.
That may or may not account for the number of shoehorns I own.
