(global-set-key (kbd "<C-return>") 'org-insert-item)

<C-return> runs the command cua-set-rectangle-mark (found in
cua-global-keymap), which is an interactive autoloaded Lisp function
in ‘cua-rect.el’.

It is bound to <C-return>.

[Arg list not available until function definition is loaded.]

Start rectangle at mouse click position.