Looks like others of you are confusing the terms "resident" and "citizen."
If I were going to discuss my packweight for "awesome summer trip 2010" you would want to know location, weights, and generally have some other bits of info.
If you are going to discuss "stop and identify laws" make sure you have the basic info on some standing federal and state law, and can define the common terms with their legal terms. I think things are getting mixed up in here because of it. :(
A U.S. citizen does not need to carry ID at all times, but certainly under many situations it is beneficial, or required.
A U.S. permanent resident, not to be confused with a citizen, must carry one at all times.
EDIT: I saw a post by Justin Taul that said,
"Anyone here who thinks they are required to carry ID is completely mistaken. There is not one federal law in existence that requires it."
Unless he is only referring to U.S. citizens, I was going to link the standing Federal statute requiring U.S. permanent residents to have their valid identification present on them at all times.
But, the url is long (cannot remember how to hotlink here), and I gotta run. If you are interested, and want to verify, you can visit our U.S. Immigrations website below.
Apologies to Justin if you did not mean residents. If you did, below is proof to the contrary.
From website www.uscis.gov:
"A green card is issued to all permanent residents as proof that they are authorized to live and work in the United States. If you are a permanent resident age 18 or older, you are required to have a valid green card in your possession at all times. "