Show both staged & working tree in git diff?

If you mean the changes between the working tree and your HEAD commit (i.e. both staged and unstaged changes together) this is just done with:

git diff HEAD

Is there a way with git diff to see all in one go?

There is, with Git 2.4.0+ (April 2015).

See commit 4055500 from Michael J Gruber mjg:

commit/status: show the index-worktree diff with -v -v (or -vv)

git commit and git status in long format show the diff between HEAD and the index when given -v. This allows previewing a commit to be made.

They also list tracked files with unstaged changes, but without a diff.

Introduce '-v -v' (or -vv) which shows the diff between the index and the worktree in addition to the HEAD index diff. This allows a review of unstaged changes which might be missing from the commit.

In the case of '-v -v' (or -vv), additional header lines

Changes to be committed:

and

Changes not staged for commit:

are inserted before the diffs, which are equal to those in the status part; the latter preceded by 50*- to make it stick out more.

In the OP's case, a simple git status -v -v (or git status -vv) will show both staged and unstaged diffs.