DO NOT USE THE CARD UNTIL YOU NEED IT AS BELOW
Download "Restoration" ( www.snapfiles.com/get/restoration.html ) and install it. Insert your card into a card reader (should work if connected "in camera", but never tried) and use Restoration to search the card for deleted files, saving to somewhere other than your card. I've recovered virtually every picture on a card this way, your mileage will vary.
Once done, make sure you back up the pictures to (preferably) a hard disk or CD/DVD. I wouldn't recommend keeping pictures on a card that you use in a camera, if you want to carry them around with you invest in another display device.