What are your favorite, must-have but inexpensive (say, under $5 or $10 per user) office supplies? The kind of thing few (if anyone else) use but you can’t do without?
Mine is printer-fed 2-inch tab inserts. Made for 5-cut hanging file folders but there are tabbed binder dividers that use these, too. Cleaner than writing them by hand, simpler than trying to cut them out of paper, less messy than trying to apply tiny adhesive labels and less maddening than using a handheld label maker. (All of which I’ve done before.)
Avery and Pendaflex (#43290) make them, but I notice they usually have to be ordered. About $2 per 100 inserts.