The clipboard is just an area of RAM designated to act as a clipboard, there's no physical or programmatic "clipboard". Your only accesses to the clipboard are copy, cut and paste. So if there's something in it, paste it somewhere. If there's nothing in it, copy or cut something to it. (Cut is just copy, then delete from the original location.) And when you restart the phone, or turn it off, the clipboard is cleared.
If you need more that just the one clipboard location, install something like
Clipper - Clipboard Manager - it maintains its own internal "clipboard" that keeps what's in it through restarts and power-offs - and can hold more than one ting at a time that you get to choose from. (But it's still only copy, cut or paste.)