Somewhat un-guixy-but-easy way to get started in:

    $ mkdir -p ~/profiles
    $ guix package -p ~/profiles/developer -i gcc-toolchain gfortran-toolchain emacs
    $ guix shell -p ~/profiles/developer --check
    (env)$ cd yourproject # which has guix.scm inside
    (env)$ emacs
    (have emacs do "guix build -f guix.scm" in there from time to time)

This creates a new profile "developer" (you might want that to be more granular eventually, but whatever) with the 3 packages inside and then starts a shell inside that profile. You will have access to those inside that shell (only guarded by PATH etc), but you will ALSO have access to all the tools-outside-that-shell.

If you want to containerize, you can do that, too. Note that then you won't have any of the usual packages, including coreutils, available (no "ls" :) ):

    (env)$ exit
    $ guix shell -C -p ~/profiles/developer --check
    (env)$ ls
    sh: ls: command not found
    (env)$ exit
    $ guix package -p ~/profiles/developer -i coreutils
    $ guix shell -C -p ~/profiles/developer --check
    (env)$ ls

It works!

    (env)$ guix
    sh: guix: command not found

Well, that can't be good.

    (env)$ exit
    $ guix package -p ~/profiles/developer -i guix
    $ guix shell -C -p ~/profiles/developer --check
    (env)$ guix build -f guix.scm

It works!

Note that the "-C" automatically also exposes the current directory that "guix shell" saw when starting up to the container.