I have a zip file, within it I have another zip file, and within that file I have a txt file. When I unzip the outermost file with Apple's archive utility, it unarchives the inner files automatically. Is there a way to prevent this from happening?
The Archive Utility has a Prefs panel - though it's not obvious how to get there.
The app itself is in
/System/Library/CoreServices/Applications. Go to that folder, launch the Utility by double-clicking, then under the app name in the menu bar, choose Preferences.
Uncheck 'Keep expanding if possible'.
There is a way to expose this pref panel in the regular System Preferences Panel, which needs something like TinkerTool to activate.