Vim Tips Blog : Programmer Productivity Tips

The Control-R mechanism is very useful:-
:h i_CTRL-R

Usually used for inserting the contents of a register 0-9a-z
but can also insert the following special registers etc

'"' the unnamed register, containing the text of the last delete or
yank
'%' the current file name
'#' the alternate file name
'*' the clipboard contents (X11: primary selection)
'+' the clipboard contents
'/' the last search pattern
':' the last command-line
'.' the last inserted text
'-' the last small (less than a line) delete
=5*5 insert 25 into text (mini-calculator)