I hope this never happens, but if you're ever in a stuck elevator, a heavy traffic jam, or a hostage in a bank robbery gone bad, you'll need something to help the time pass.
So, as a public service, here's some bits of trivia you can share in case you don't have a good book or your Ipod runs out of juice.
After Steve Rogers ingested the Super-Soldier formula and became Captain America, he was given a bulletproof triangular shield. Soon after, he was given the now-familiar round version. Here's some of the history behind it.
American metallurgist Myron MacLain was given the task to create plating for armored fighting vehicles. He took a mixture of steel alloy and Vibranium [a rare metal that can absorb and release energy such as sound waves] and attempted to cast the mixture.
Unbeknownst to MacLain, the mixture was somehow contaminated. That contamination resulted in a one-time casting of a concave disk. MacLain tried again and again to repeat the process, with little success. In fact, it was one of his failures that gave the Marvel Universe adamantium, the same material that composes Wolverine's claws and bones. It's a long held myth that Captain America's shield contains adamantium.
The shield's properties are quite unique. While it weighs only 12 pounds, it is essentially indestructible. It can withstand the force of an enraged Hulk, and even the full-on impact of Thor's enchanted hammer. Cap can also throw the shield with uncanny accuracy, and has such familiarity with it that he can carom it off almost anything and know exactly where it will go.
Cap has been forced to use substitute shields over the years, including pure vibranium and adamantium versions. The spy agency S.H.I.E.L.D[coincidence] tried to upgrade Cap by outfitting him with a photonic energy version. It had a 'flexible containment matrix' that could transform it into a staff or sword weapon.
Tips of the nerd cap to Wikipedia, The Star-Spangled-Site, and The Marvel Directory.