Is there a way to switch selection via hotkeys? Say, I've created just a cube and a cylinder and now the cube is selected. Is there a hotkey that switches selection to the cylinder?

I guess, the order of switching (if there's more than 2 objects) may be different like switching between tabs in a browser: "by usage" and "by creation order", the former being more helpful. Switching between objects would decrease mouse/touchpad usage tremendously. I guess, there's either some "history of selection" object in the Blender core and this is implemented or this is not implementable without changing the core.. but I may be wrong.

The same question may be asked about switching between faces/edges/vertices of one object, but let's start from the switching between objects.
CtrlI inverts your selection.

That is, anything currently selected becomes unselected; anything unselected becomes selected.

That will include any cameras and lights you have on the current layer.