Here is how to have a quick look into any file in your git repository without checking it out or overwriting your working copy.
git show master:path/to/file/file.xml
This will show file.xml of the master branch. Git will echo the contents of the file to the standard output. So to actually save a temporary copy of the file for inspection you can just redirect the output into a new file:
git show test:path/to/file/file.xml > temp_file.xml
or pipe it into your favorite editor like this
git show test:path/to/file/file.xml | vim -
You can even look into files in the origin repository:
git show origin:path/to/file/file.xml
There is a lot more you can do with
git show like showing diffs. Check out
git help show for more information.