There are a few coin tricks out there using gimmicked coins which I use on a regular basis. The reason I use coins is because pulling out a pack of cards in a bar or club is a bit strange whilst everyone in a public venue will have coins on them.
To introduce them to the girl the opportunity presents itself when she asks "What do you do?" Tell her your real job and say "but I'm also a magician" (strictly speaking you are)
99.9% of the time they will reply "show me some magic then"
Take the coin(s) out of your pocket and do the trick.
The best trick coins are the "Bitten coin" where you bite a piece off a coin (in the UK a fifty pence piece) then spit it back out onto the piece in your hand. (a lot of the time people will say "Let me see the coin" afterwards so you need to learn the "french drop" to switch a real coin for the gimmiked one :TIP make full eye contact when you perform the French drop it diverts attention.)
The best of all however is sold in England under the title "coin unique"
There are a lot of tricks you can do with this but the main ones are...
You hold a one pence piece and a pound coin in your hand, close your fingers, open them up again and the penny is gone (If you can previously plant a penny on the girl to find later all the better)
Best of all: You put a penny and a pound coin under a glass, swirl it around and the penny vanishes in front of your eyes -this gets brilliant reactions!-plus you can hand out the pound coin for examination afterwards.
I think these tricks are available in a lot of different currencies try this site if you are in the UK
http://www.magictricks.co.uk/
As a footnote : just after the trick, the confusion caused will make the girl very suggestible for a brief few seconds to any idea you wish to plant in her mind ;Comfort, arousal etc.