First thank you for this very useful tool.
I LOVE clipboard managers ;-)

Here is a VERY interesting feature I used a lot with other clipboard managers (klipper in kde or ditto in windows) :

When the popup is shown, you can type some text, and as you type, the list shown in the popup is automatically filtered to show only the records matching the stuff you have typed.

Example, I show the popup by clicking the icon or triggering the command xfce4-popup-clipman, I got hundreds of data, then I type "iwconf" and as I type, the list reduced to finally show all the records containing the string iwconf

To avoid the filter to be done actually in real time and consuming a lot of cpu, an additional idea is to wait that at least 500ms are gone without any key pressed before executing the grep.

Another additional data : you could manage special keys, like the backspace key to remove the last letter of the filter, or the escape to clear the entire filter.

Thank you very much :-)