I only carry the necessary's in my wallet (DL, Medical, Amex, Debit), those 4 + my Medallion card. I use my Medallion card 3-4 times each trip:
- Kiosk swipe
- Skyclub entry
- Boarding 1st leg
- Boarding 2nd leg
1 card that works for everything you do at the airport, why wouldn't you carry it.
Note: I don't use the DM bag tags, so carrying the card for me is insurance if anybody ever asked to prove my status (check in line nazi's).