I dunno about others, but I sure do! I have CSS stylesheets in 7 colour themes, a dozen bootstrap-like JS plugins that add common interactive elements I can drop into any site,
and tons of parts and pieces of layouts (like an order form, signup form, pricing chart, or media player) isolated and ready to re-use.
I also maintain a big snippets file, filled with HTML, CSS, JS, and command-line snippets and tricks so I can grab them from anywhere.
I dont know how any freelancer or contractor doesnt have a bag of tricks like this.
My responsive testing tool is located at: https://github.com/tomhodgins/speedtest You can use your keyboard keys 1-0 to test a variety of widths quickly, or use the buttons on mobile to test widths your phone or tablet can't physically emulate
You can also check out my CodePen profile, here's my collection of 'Front-end snippets', but I've got plenty more on there you can feel free to use or expand on: http://codepen.io/collection/nNqyvZ/
I also maintain a big snippets file, filled with HTML, CSS, JS, and command-line snippets and tricks so I can grab them from anywhere.
I dont know how any freelancer or contractor doesnt have a bag of tricks like this.