Small BIFL items are highly dependent on the individual. I own a couple nice pens that I have had since I was a kid. I never use them just because I rarely need a pen and therefore don't carry one with me. If you almost never use a pen, a disposable Bic is BIFL (I've got one or two that are well over 10 years old and still going)

For me, that item is a Lever card multi tool (TSA safe wallet card). I mostly use it as an emergency screwdriver, staple remover, and size reference when taking pictures of things.

The key is that it has to be something they need on a daily basis, and the BIFL version needs to perform better and more reliably than the disposable version (lighters come to mind here; a disposable that that has been sitting in a drawer for 2 years will still work just fine, but a Zippo will be bone dry)