If you are travelling to USA with electronic devices (e.g. laptop, mobile phones, Ipod, music / video player, or others), please note that Obama has given the airport customs the rights to seize your electronic devices for a few days and search your files, including deleted files, WITHOUT SUSPICIOUS. If your devices consist of pirated or illegally downloaded videos / musics or other illegal contents, you will be in trouble.
Delete your files before you go to US is useless, as they can be recovered.
Possible solutions:
1. on your laptop, install Truecrypt (open source, cross-platform,
http://www.truecrypt.org/) or FreeOTFE (open source, available on Windows and Windows mobile only,
http://www.freeotfe.org/). These 2 software let you create virtual partitions which you can store your files. You will need passwords to open/mount the virtual partitions.
2. And, use KillDisk (http://www.killdisk.com/) to Wipe the free space on your storage devices. Because, if you move your files to the virtual partition created by Truecrypt or FreeOTFE, the word "move" in computing actually means "copy the files to another folder then delete it from the original folder", deleted files can still be recovered from the original folder. That is why you need to wipe the free space of your storage device.