Can I copy SD cards using an iPod touch? I'd like to backup photos taken on my dSLR camera on SD cards. Can I use a USB adapter to copy an SD card into the iPod's local memory, then attach a different SD card and copy the files to that?
Probably not, as the Apple iPad Camera Connection Kit is officially not supported on iPhone or iPod touch; and that would just give you the physical connection of your SD card to the iPod touch. 

To have direct access to the file-system of your SD-card you need a jailbreak.
There is a slight chance you may get the Apple iPad Camera Connection Kit working on a jailbroken iPod touch:

Check out iConnectionKit and this YouTube video.


  Camera Connection Kit on iPhone / iPod Touch (upcoming JB tweak)
  
  PROJECT STATUS = ALPHA
  
  Top 5 contributors will be granted early beta access on 2nd of April 2012.
  
  SUPPORTED DEVICES - iOS 5.0.1
  
  
  iPod Touch 4G - [Tested &amp; Working] - Watch the demonstration videos.
  iPod Touch 3G - [Possible] Contribute any amount to help us afford the device and enable the Camera Connection Kit
  iPhone 3GS - [Possible] Contribute any amount to help us afford the device and enable the Camera Connection Kit
  iPhone 4S - [Possible] Contribute any amount to help us afford the device and enable the Camera Connection Kit
  iPhone 4 - [Possible] Contribute any amount to help us afford the device and enable the Camera Connection Kit
  
  
  JB required.