Bookmarklet to populate your clipboard with preset text by clicking the bookmarklet.

bookmarklet

javascript:(function()%7Bcctb_t%3Ddocument.createTextNode(%22Replace%20this%20text%20with%20the%20text%20you%20want%20copied!%22)%3Bdocument.body.appendChild(cctb_t)%3Bcctb_r%3Ddocument.createRange()%3Bcctb_r.selectNode(cctb_t)%3Bwindow.getSelection().addRange(cctb_r)%3Btry%7Bdocument.execCommand('copy')%7Dcatch(err)%7Bconsole.log('Clipboard%20Copy%20Text%20Bookmarklet%3A%20Error%20in%20copying.')%7Ddocument.body.removeChild(cctb_t)%3Bdelete%20cctb_r%3Bdelete%20cctb_t%7D)()

copyText.js

// Create the text you want copied.
txt = "Replace this text with the text you want copied!";
// Please don't use this to store your passwords.

// Simulate a text selection in the browser.
//  1. Create a text node and append it to the active page.
console.log("Clipboard Copy Text Bookmarklet: bookmark pressed.");
var txt_node = document.createTextNode(txt);
document.body.appendChild(txt_node);

//  2. Create a range over this text.
var range = document.createRange();
range.selectNode(txt_node);

//  3. Tell the window to create a selection of this range.
window.getSelection().addRange(range);

//  4. Perform copy.
try {
  // Now that we've made a selection, execute the copy command.
  var successful = document.execCommand('copy');
  var msg = successful ? 'successful' : 'unsuccessful';
  console.log('Clipboard Copy Text Bookmarklet: Copying of text was ' + msg);  
} catch(err) {
  console.log('Clipboard Copy Text Bookmarklet: Error in copying.');
}

// Remove the added text node and delete variables.
console.log("Clipboard Copy Text Bookmarklet: Cleaning up.");
document.body.removeChild(txt_node);
delete txt_node;
delete txt;