Just your standard congratulatory card for any occasion that calls for a drink. Hell, you can force this into just about any situation. Kindergarten graduation? Congratulations shot glass cards for everybody. Ok, seriously don't do that. That was a joke. You'll go to jail.
The Bottle Hanger Card
The card features a diecut circle at the top to attach it to all sizes of bottle (even the enormous Absolut bottles if you mean serious business).
If you know the party you are going to is already stocked, or you have to send via post, perhaps a regular card is more in order. Each A2 card comes with a matching white envelope.
The below video shows the Shot Glass Card being assembled. It features The Very First Birthday Shot Glass card design which is the same premise but different design.