I have the list in my REX, but I do carry a PHOTO COPPY of the cards (all on one sheet, front and back, reduced during copying) and I carry my WN card.

If I am going to be doing a lot of one airline or hotel, I stick the card in my wallet.

I have one of those vinyl business card holders, with 4 section plastic sleeves. Free promo item from Zofran ondansetron HCI, whatever that is. It's holding 8 hotel cards, 4 airline cards (3 others I keep in my wallet), 4 rental car cards, 3 frequent shopper grocery cards (No Safeway within 500 miles of here!). Between the sleeves, I have airline bump vouchers, upgrade coupons, companion certs, SOS and other employee recognition cards, a copy of Delta Dollar rules, car coupons, hotel and car certificates, a copy of my birth certificate, passport and one visa. This rubber-banded holder stays in my carry-on travel bag and has come in handy many times.

As noted by other posters, you hardly ever need to have the actual card (with the exceptions being Southwest and Hertz #1 Club Gold, I guess) I find it reassuring to have them with me anyway. I always put the cards for the programs I know I'll be using on any one trip in my wallet. But I also put the cards for favorite programs and programs in which I have elite status in my carry on.

I know that AA Reps can also slide your AAdvantage card through a reader on their keyboards to bring up your information. I typically give my card to them when I check in but they rarely use it. They seem to prefer to key in my last name (it's short!) or the record locator number.

A while back I was checking in for an AA flight and the Rep needed to call the AAdvantage department to confirm something. He asked for my AAdvantage card to get the phone number for the AAdvantage desk--because it was easier than looking up the number on the system!

I pride myself on my light packing--but I feel these cards take up very little space and occasionally come in handy. I also carry a list of all of my important numbers on a laminated card--and stored in an internet storage account. I also always bring my passport (and several photocopies) even on domestic trips--because you just never know!

I have never needed my Hertz #1 Gold card when picking up a car. I can't remember ever being asked for it, over probably more than 100 rentals as a #1 Gold customer. Leave it at home, IMHO.

I had problems getting upgraded at 3 Hiltons in Italy last year because I didn't have my HHonors gold card with me. I had the number but they were very rude regarding my lack of a card. No problems in Munich though.

I carry cards for US and AA (my two most frequent carriers) to use in e-ticket kiosks. Although you can use any credit card, using your FF card sometimes saves the extra step of entering your FF number to confirm your account.

If you put your credit card in a US kiosk, for example, you have to enter one additional piece of information -- either your FF number, your flight number, or something else I forget. If you put in your US card, on the other hand, you go straight to your reservation.

Also, as mentioned earlier, flashing your card is the easiest way to prove you're entitled to be in the preferred line (although truthfully, I have not once been challenged on why I was in a preferred line).

Admirals Club
Suntrust Bank Card
Suntrust Debit Card.
Citibank AAdvantage Debit Card.
TDWaterhouse Debit Card.
Grindlays Standard Chartered Debit Card.
Citibank AAdvantage Credit Card.
AAdvantag Executive Platinum Card.
Delta SkyMiles Medallion Card.
United MileagePlus Premier Executive Card.
Hyatt Gold Passport Platinum Card.
Starwood Preferred Guest Gold Card.
Marriot Rewards Card.
Leaders Club Card.
Wyndham ByRequest Card.
Hilton HHonors Gold Card.
AAA of NY card.
Phone cards.
NYC Metro Card
DC Metro Card
Chicago Transit Card.
London Tube card.
And multiple business cards.
Drivers License.
Social Security Card.
Health Insurance Cards.
[and a few more nicknacks that comprise my wallet-like card holder.]