Have you ever found yourself running late to a birthday, graduation, wedding, and still needing to buy a card along the way? We keep blank greeting cards in our car's glove compartment, along with a pen, so that we can just pull one out and write up an appropriate message inside the card while we're on the way to the event.
We usually find blank cards in packages of 8, 10, or 12, with matching envelopes included, and with an attractive but generic design on the front, suitable for pretty much any occasion. Abstract nature-type designs in pastel blues, yellows, or greens tend to work for everything.
We had this happen a few months ago and were relieved to discover that a Goodwill store near the party had greeting cards for sale! With little ones in the house, we're always running late, so keeping a few cards (and a pen!) in the car will improve our odds of being on time.
By the way, the card pictured here is made out of elephant dung. I thought you'd appreciate that.