"groups of files" in Git?

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