Cuttables are characterized by adhesive-backed strips or sheet material that can be cut by hand. I prefer an Exacto craft knife using a #14 blade. Examples are masking tape, shelf liner, and detailing tape or pin striping, as found in an automotive supply store.
Industry-specific resists made of vinyl or soft rubber are staples and come in a wide variety of thicknesses and widths. Most can be found at stained glass supply sources, both retail and online. A plotter to cut the resist and an artistic software are a great asset for the stiffer and/or thicker resists.
Another great option is the pre-cut stencil. There are some splendid sources to order from.