I have made a few custom bookmarklets that I bring to my internet experience. These allow me to perform a few tasks that I do on a regular basis in one step rather than copying, surfing to a new page, pasting. These are bookmarks for productivity.
This one takes me to the Internet Archive Wayback Machine page for the current site I’m accessing:
javascript:void(location.href="https://web.archive.org/web/*/"+document.URL.split("://")[1]);
This updates the Amazon.com product page to one with my affiliate link, like for this Hard Drive I just bought.
javascript:void(location.href='http://www.amazon.com/dp/' + document.getElementsByName('ASIN')[0].value + '/?tag=000703-20')
This one uses a Google API to creates the QR-Code for the web page you are visiting.
javascript: location.href='http://chart.apis.google.com/chart?cht=qr&chs=350x350&chl='+escape(location.href);
Camelcamelcamel is a great service that charts the Amazon.com price of all products so you can see if you are getting a good price. This bookmarklet can take me there in one step.
javascript:void(window.open('http://www.camelcamelcamel.com/product/' + document.getElementsByName('ASIN')[0].value))
I hope that these can be useful to you or even inspire you to create new bookmarklets to serve your purposes.