I have general rules of thumb for things where there isn't room in the interface for a specific button to a function.
- Tooltips should be everywhere possible.
- Ctrl/Cmd is for extra functionality (ie: more control) The keyworder for example now limits the 'Copy to Clipboard' to only the first 50 keyword if you hold ctrl
- Shift is always for a change to the way that functionality works (ie: it's a shift in what it does).
- Ctrl-Shift is always destructive.
I always try and avoid using Alt as most OSes use it for something system-wide and it's position close to the space-bar makes it unnatural to reach (one of the main reasons I don't like my Macbook is because of the Cmd button placement).
If you need to do something, and there isn't a button for it, try mousing over other buttons. If it's still not there, let me know and I'll add it