If you're looking for effects that can pack into your wallet, I highly recommend any (or all) of the following items. I know you said you prefer mentalism style presentations, but I think these deserve mention as far as your requirments go. They're all perfect for walkaround, and they all pack right into your wallet (and since they're all credit cards - they look perfectly normal in there).
James Ford's line:
No Credit -
http://www.elmwoodmagic.com/?nd=full&key=2426 An examined credit card is displayed in right under the noses of your spectators, you wipe the numbers right off the card. The now blank card can be examined immediately.
Messy Business -
http://www.elmwoodmagic.com/?nd=full&key=2427 Similar to No Credit except this time the card is shaken and all of the images and numbers tumble around on the card (Think the finale to Presto Printo with a credit card)
Credit Card Monte -
http://www.elmwoodmagic.com/?nd=full&key=2425 - The old two card monte using a credit card and video card membership
Bet On It -
http://www.elmwoodmagic.com/?nd=full&key=2428 - Examined credit card is offered as a prize if you can't find a selected card. Selection is made and lost into the deck. After being unable to find the card the magician asks the spectator to turn over the credit card (which you can have them hold if you like). The small pic of Abe Lincoln on the front is now holding the selection!
Bending Credit Card -
http://www.elmwoodmagic.com/?nd=full&key=2429 - Self explanatory.
Menny Lindenfeld -
Safety Hole -
http://www.elmwoodmagic.com/?nd=full&key=3172 - A Credit card is shown to have a hole right through the magnetic strip. The magician explains he can move the hole in order to use the card. With a quick shake the hole moves to the other side of the card, leaving the magnetic strip whole once more. With another shake the hole slides back over the strip. Explaining that sometimes this isn't enough security, the magician shakes the card one more time and now there are three holes through the magnetic stripe. The card can be handed out for immediate inspection. Basically, this is like Hollow with a credit card. Very cool effect.
Bite-off Credit Card -
http://www.elmwoodmagic.com/?nd=full&key=3173 - Just like a coin bite.
Brad Manuel
Credit Card Fraud -
http://www.magicbox.uk.com/shop.php/shop/magic-tricks/close-up-magic/credit-card-fraud/p_466.html - Borrow a credit card and watch their eyes go wide when you start to peel the magnetic stripe off of the card! After playing with it a bit you rub it back onto the card and immediately hand it back to them. This is a quick-hit effect but it hits HARD. Some of my favorite reactions have come from this little gem. Ever since getting this I have never left home without it.
So there you go. 8 effects that can pack right into your wallet. Yes there is some repetition (No Credit and Messy Business) so I would say get one or the other. However, you can't go wrong with any of them (I think). With a little thought, these can be given a "mental magic" (sorry Mr. Browning) air - dealing with false perception and the idea of controlling the spectators sense of sight and/or touch (pm me for ideas on how this can be done).
Just in case you're wondering - none of these effects require advanced sleight of hand skills, so from a technical standpoint they can go right into your act almost immediately.
Good luck to you.