on USCIS website many years ago it give instructions saying PRs do not need to carry the GC, then they remove that
and replace with soemthing like "You should be able to repsent the GC within resoable time frame when requested"
Laws that requirs PRs to carry the GC is called INA 264 (or 8 USC 1304 Under United States Code).
Read teh following. In theory if you spend 5 years as PR and then apply for citizenship anmd during teh interview the
IO ask you "Have you always carry your GC in the past 1500 days?" You anwser I never carried it, the youconfess to
1500 coutns of violation of 8 USC 1304 and subject to 1500*30 daysd in jail and af ine of $150000.
But practically, you are overally better offf if you only carry a photocopy. A little more caution you can carry photocopies
in daily lives and only carry real GC when travelling more than 100 miles from you home or stay overnight away from your
home plus when visiting some sensitive area like airport, nuclear power station, border region, military bases etc.
When you make a photocopy and carry it, make sure to write "This is only a photocopy of the original permenent resident card"
legend on your photocopy to fend off potential forging charge
http://law.onecle.com/uscode/8/1304.html
(e) Personal possession of registration or receipt card; penalties Every alien, eighteen years of age and over, shall at all times carry with him and have in his personal possession any certificate of alien registration or alien registration receipt card issued to him pursuant to subsection (d) of this section. Any alien who fails to comply with the provisions of this subsection shall be guilty of a misdemeanor and shall upon conviction for each offense be fined not to exceed $100 or be imprisoned not more than thirty days, or both.