As pointed by Phone Boy, the N93 lens cap strap is very nice but it's not obvious. It's on page 15 of the English language version of the N93-1 manual. I figured it out right away because I am paranoid about smudging the lens! And also very absent minded so a lens cap without a strap is useless to me.

Anyways here's a photo (taken with the N73's fantastic macro mode) that illustrates how to attach the lens cap strap: