Although the iPod Touch 4 does not have a built-in GPS receiver and chip, there are ways to add this functionality. It appears the OP has ordered a GPS add-on kit and extended battery kit, so many of the previous posts are pointless.
I have an iPod Touch 4, as well, and here is what I have found with regard to using it as an outdoor device:
-most of the GPS hardware add-ons are more suited for vehicular use than trail. That is, they hang off like a tumor, or are connected via a cable, but aren't really a great all-in-one trail-ready package
-It is quite possible to use GPS apps and download maps before going out, so you don't need wifi. In fact, when you go out be sure to turn the wifi radio off or it will eat more battery.
--I haven't found a map and app combo that I really love, but I also haven't tried them all. Seems like Steve Pratt's advice about trial versions is right on
If you (and I) had an iPod Touch 3, then I would purchase the Magellan Toughcase. It is a waterproof case with a GPS chip and extra battery built in that still lets you use the touchscreen. In fact, I've been waiting for them to come out with a version compatible with the 4 for quite a while, but I don't think they will. I've looked for a cheap iPod 3 that would be my outdoors device (mated with a Toughcase), but haven't found a good enough price to make me bite. http://www.magellangps.com/lp/toughcase/index.html
More information and useful links on navigating with a iTouchhttp://gps.about.com/od/mobilephonegps/a/iPod-Touch-GPS.htm