Can I use my iPod classic to store photos for my Canon 5D MkII?
Yes.

You need the discontinued "iPod" camera connector. (not to be confused with the iOS iPad camera connector)


http://support.apple.com/kb/TA38187


They are for sale on Amazon (and of course at local thrift shops and electronics shops worldwide).

http://www.amazon.com/Apple-Camera-Connector-iPod-White/dp/B000KIRGF4