The iPod can only be synced with one iTunes library at a time. If you try to sync content to it from another iTunes library, everything will be erased from the device and replaced with what is in the new iTunes library. The only way to add content to the iPod from multiple libraries is to manually manage the iPod's contents. See this article for more information.
When you return home, you can always transfer purchases you have made and added to the iPod by choosing File -> Transfer Purchases from <name of iPod>.
Thanks that is important to know. I really am only concerned with transferring any new iTunes Store purchases/downloads that I might make to the iPod while away. It sounds like that might be more involved from the description in the linked article, or maybe not. I guess I will just have to try it to find out. Thanks again.