Clipman is a clipboard manager for XFCE. There is also a plugin for it that can be used to integrate it into the XFCE Panel.
To install Clipman and its panel plugin:
$ sudo apt install xfce4-clipman-plugin
I like to have Clipman plugin always around in my Panel. To do this, right-click on the Panel, choose Panel -> Add New Items and add Clipman.
Some of its settings that I configure:
Increase the number of copied items in history
Enable sync selections. This connects clipman to the default X11 clipboard. If not, only stuff you explicitly copy can be explicitly pasted. Middle-click to paste will not work as expected.
Choose to paste instantly on
Shift + Insert. This means that when I click on an item in history list, it is directly pasted into my last focused application.
Tried with: Clipman 1.2.5-1 and Ubuntu 14.04