When you enter the Casino, straight ahead of you, past the car, is the bar. When you go to the bar and order a cocktail, you'll see the list. When you hover over each of the cocktails you'll see instructions on how to unlock the ones you do not yet have. Simply complete the objective given to unlock the cocktails.
The same goes for the emotes. When you are sitting at a Poker Table, hit either or to bring up the emotes. Follow the instructions for each one you don't have in order to unlock them all. Once you've completed all of the objectives and have them all, the achievement is yours.