Checkout first version of each file?

Hello,

My "issue" comes with my usage of git at work. I work with lots of
applications, each of them part of each system. There are lots of
processes and lots of subsystems, so I never clone the entire repo
into GIT, since it could be painful and slow. Even if I do so,
everyone else is using ClearCase, and their changes cannot be included
into my git repo until they "chickin". Sometimes, I must update
sources from FTP because the changes are not up to date in
ClearCase...

So, I clone every file that I will need to work into GIT, so i can
work with these files having a better control (With ClearCase it's a
foolish "checkout>>lots of changes>>checkin" flow). But sometimes I
don't know how many files I am going to change until I start coding
the requisites.

In this cases, there is a situation that I don't know how to handle.
If I need to rollback every change made to every file I cannot just
checkout the initial commit, cause I've added files after that, and I
need their initial versions too.

So, how can I checkout the first version of each file? (I know that
GIT tracks contents and not files, but the fact is that I need to keep
track on files, it's the real thing I work with)

pd: Sorry about my Argentinian-English (if it sounds so)

Thanks,
Dario