If, at any point in the last two or three years, I needed to draw a simple UI icon it's gone into Just a Few Icons. It's a collection of SVG icons that can put into a sprite easily and have it ready in your project using the symbol syntax, making them a really portable set of icons.
Having a portable set of icons like this has been really useful in prototyping, because it can inform pieces of a UI, whether an icon adds value or meaning to a user, whether that particular icon is communicating well and just having a base set to swap in and out makes that process more focused on the task versus the process.
Choosing to setup this icon set in this approach makes icons easy to style their fill color or stroke and size. Whereas icon fonts aren't nearly as adaptable in that regard.