This is quite easy with help of standalone package:
% other package which you use
Experience you write as
.. other used packages
<content of your file>
On this way you can compile each file independently and use in the main file (as stated David Carlisle in his answer, when you like to form complete document.
Edit: For details, how to use
standalone package, see the manual of package. There is describe more scenarios, how to use them. Of course, you can make simple text files without of possibilities of their compilation outside of main document.
The CV is usually short document, so its dividing into more (sub)files is not very sensible, however, if you do so, than their direct compilation become handy.