"groups of files" in Git?

[Nikolay Shustov <nikolay.shustov@gmail.com>]

Hi,
I have been recently struggling with migrating my development workflow
from Perforce to Git, all because of the following thing:

I have to work on several features in the same code tree parallel, in
the same Perforce workspace. The major reason why I cannot work on one
feature then on another is just because I have to make sure that the
changes in the related areas of the product play together well.

With Perforce, I can have multiple changelists opened, that group the
changed files as needed.

With Git I cannot seem to finding the possibility to figure out how to
achieve the same result. And the problem is that putting change sets
on different Git branches (or workdirs, or whatever Git offers that
makes the changes to be NOT in the same source tree) is not a viable
option from me as I would have to re-build code as I re-integrate the
changes between the branches (or whatever changes separation Git
feature is used).
Build takes time and resources and considering that I have to do it on
multiple platforms (I do cross-platform development) it really
denominates the option of not having multiple changes in the same code
tree.

Am I ignorant about some Git feature/way of using Git that would help?
Is it worth considering adding to Git a feature like "group of files"
that would offer some virtutal grouping of the locally changed files
in the checked-out branch?

Thanks in advance,
- Nikolay