Last week we all got new security keys to the building where I work. The keys are business-sized cards with a computer chip in them. You wave it in front of the security panel, and the door unlocks for a few seconds. Sounds good, right?
Not when it's 10 degrees and windy, and you've got the thing in your wallet, in your purse which is over your shoulder behind your laptop bag. Have to stop, put everything down, remove gloves (remember it's 10F with VERY STRONG WINDS), find card, gather bags, wave card, open door.
Ergo, a lanyard. Leftover piece of binding, metal clip from stash of findings, and about ten minutes at the sewing machine. I made the thing extra long so I don't have to take it off to wave it in front of the security panel (which is mounted just above my eye level).
Works like a charm.