I'm traveling this week. I now carry two iPods. My trusty 120 GB Classic that has my entire collection. Plus, my trusty 8 GB Touch I use for browsing the web and playing games anywhere (plus there's some music there).
I had an issue today where I used a code on my iPod Touch to download some free music from iTunes. The iPod went into sleep mode while it was downloading and cut off the download midstream. The first thing I did to address this was go into Settings > General > Auto-Lock and change the setting from "1 Minute" to "Never".
This change allowed me to download the entire play list without issue...except for the one that got cut off mid stream. I kept getting the "Download error. Tap to retry." message. This was especially annoying because the iPod Touch kept asking me to log in with my Apple ID.
To fix this, I remoted into my PC at home (using LogMeIn) where my "master" iTunes library is. I then went to downloads and clicked the down-arrow to download the pending track on my PC. Once that was done, I went back to iTunes on my iPod Touch. That cleared the issue. The only downside is that I'll have to wait until I get home to listen to the track that downloaded to my PC instead of my Touch.