Actually, it says you need to carry a WHTI compliant document. Your passport is one such document, but you may instead carry (assuming you have one) a Passport Card, Enhanced Driver's License, or Trusted Traveler Program Card (NEXUS, SENTRI, or FAST), all of which are less bulky than a Passport.
Personally, I'd probably get the Passport Card and sew it into a pocket on my top or shorts.
"They're made of latex, not nitroglycerin"
Personally, I'd probably get the Passport Card and sew it into a pocket on my top or shorts.
"They're made of latex, not nitroglycerin"