There are two lessons here. Number one: always tell someone when you leave the group to answer the call of nature, especially a large group where your absence might not be noted for awhile. This is particularly true for groups with hikers of varied ability who don't stay together. Number two: NEVER, NEVER, NEVER leave your pack! Always take your pack with you wherever you go. That way, you will never be without your survival gear.
Repeat: NEVER, NEVER NEVER LEAVE YOUR PACK!