Don’t freeze your iPod touch.
According to Apple’s website:
It’s too easy to accidentally moisten or freeze it to be too cold.
You’ll get better battery life on an iPod touch if you turn off bluetooth and WiFi when not using them. Also, notifications drain battery, so turn those off for apps that you don’t use. (Settings -> Notifications on iOS 5.)
Since it’s a fourth generation device, you have multitasking. Bring up the multitasking tray and press and hold on an icon until they start to jiggle. You can now manually quit any apps that you’re note using.
Best of luck, and don’t forget to check out my apps! 🙂