In Normal, type the following to delete a range of lines into a named register

:10,20d a

This will delete lines 10,20 in register "a. We can verify this by typing

:reg

This will show the text that was delete in register "a.

To paste the contents in "a, just type

"ap 

In Insert mode, press <C-r> and then % to insert the filename.

This technique is applicable to all registers.

For e.g. if in insert mode, you want to paste the current search pattern, you can type <C-r> and then /.

Use the quotestar register to copy/paste between Vim and system clipboard

"*yy copies the current line into the system clipboard

"*p pastes the content of the system clipboard into Vim

Yank all lines containing TODO into a register by using append operation

:global/TODO/yank A

Here, we are searching for a TODO keyword globally, yanking all lines into register a (A register appends all lines to a register).

NOTE: It is in general a good practice to clear a register before performing the append operation.

To clear a register, in the normal mode, type qaq. Confirm that the a register is empty by typing :reg and observing that a register is empty.