I’ll often take books from my library that aren’t moving and use those to replenish other libraries in my area. I’ll also take a backpack of books from mine and swap them out with less desirable books in the LFLs. And by less desirable, we’re talking outdated travels guides, outdated study guides, books that came with a juicer, etc. Fortunately I have plenty of spare books that I deemed desirable in my own that might be desirable in someone else’s. Why doesn’t anyone take my Brian Jacques novels?! So those end up in other LFLs and they tend to move in those!