We cannot be prepared for every "what if." I do see some huge first aid kits in gear lists, anticipating a 1,000 what ifs.
I carry little in my pockets. It is usually only what I am going to need in the near future and varies from trip to trip. I do have a lanyard with a microlight, vitronix classic, whistle, and sometimes a minerature thermometer. Sometimes I wear it and sometimes keep it in my pocket, and sometimes in a side mesh pocket of the pack. At night I keep it in one of my shoes.
I just am not going to get separated from my pack. When I take a rest stop, I make darn sure that the pack cannot fall of a cliff or similar. Nowadays the pack is so light, there is no need to wander off without it.
Some good comments about not choking yourself with a lanyard have been made.
I would like to point out you are probably in greater risk of injury when wearing a ring on your finger, by slipping and catching a ring finger on something. So my wedding ring goes on the lanyard. It is just easier to take the ring with me, than have a discussion about it with my wife. Also, you are less likely to lose it on a lanyard. Mine fits kinda loose, so it could fall off while digging in the pack or other activities. And for those guys who might get married in the future... get your wedding band at a big national chain jewelry store. Buy their most common style; one that is always in stock. That way if you DO lose it, it can be replaced without grief from the better half. You can probably pick one up on the way home from your adventure. And don't ask how I know this :)