Appropriate or Inappropriate?

I flew home this past Tuesday for a grad school interview. I drove into Salt Lake City and parked my car in the Diamond Parking Lot and hopped on the bus that took me to the airport. It was 5:30 in the morning, so I was a little out of it, but I was awake enough to notice the tip jar on the driver's dash board. I peeked into my wallet and realized I had zero cash on me. Suddenly, I was faced with a predicament. I couldn't leave my credit card or my debit card. I had to ask myself, and text my sister, "Is it appropriate to leave a tip in the form of a gift card if you don't have any cash on you?" The only other 3 options: a) Wal-Mart gift card with an ending balance of $68.91 (not likely I was leaving a $70 tip...) b) Borders gift card with a balance nearing $1.00 (I think it actually had like .56 cents or so) c) Dairy Queen gift card for $2.82 So, what did I do? I did what any white girl with three carry-ons-- carrying them by herself without any help getting on or off--would do. I took a free water out of the cooler in the back of the bus as four or five other businessmen got on the bus, prayed that one of them would tip the driver, and was the first one off the bus when we approached the Delta Airlines curb.