Something that is common in some cad software that works really well is using the way a selection box is drawn to change how it selects objects.
So, for example, if you draw a box from top left to bottom right, then this would select everything fully enclosed by the box (as normal)
If you draw from top right to bottom left, then the box selects everything that the box touches. (and to help the box is dotted or differentiated )
It doesn't sound very obvious but it's really useful to be able to switch to different ways of selecting objects without a toggle or option or button.
just a thought