Originally Posted by
WillCAD
Another vote here for the passport card. It's usefulness is not limited to transiting TSA checkpoints; I am not a frequent traveler as most FTers are, but I have found my passport card very useful in a number of other situations where I need a second form of photo ID - it's issued by the federal government, and is RealID compliant, so it's acceptable to all sorts of government agencies and private companies. And as several others have mentioned above, it doesn't have your home address on it, which is a plus to me. It's also wallet-size, and laminated as tough as a DL, so it'll take a beating and won't dissolve if it gets wet.
I use my passport card not only for TSA, in airport lounges, and to prove I'm old enough to drink alcohol, but also for domestic hotel check in and to carry with me in the hotel if I think there's a chance of my keycard not working (for example, when I have a late checkout or multiple sequential reservations) and as an ID to have on my person in places (such as Rio) where I don't carry my wallet or passport, etc. In addition, I've used the passport card as my ID when paying by credit card in Buenos Aires grocery stores, etc. It's very useful and probably the least inconvenient form of ID to lose.
However, IIRC it's cheaper to renew the passport and passport card at the same time and since the passport card (essentially) cannot be used for international travel, I wouldn't arrange for the passport and passport card to expire at different times. I tend to renew both very quickly at my local passport office, which can be done even faster if you have proof of immediate travel or travel which requires visa applications.