I'll probably just transfer a few thousand songs on an external drive. Only because I don't have any flash drives over 8Gb . I'd like to keep a varied collection for demoing, since most meets I just bring an iPod, and I always end up regretting not having on hand that one song that you suddenly want to try with a particular piece of gear.
Don't bring an iPod, it won't do certain equipment justice. Give it flak....(flac,..ha.ha) and hopefully you get the possible sound.
I don't think there is anything wrong with bringing an external drive, if anything, you can reference anything you want and not have to worry about it after you go home. It's always nice to know what different genres of music sound like over certain sound systems.