I feel hip at the Art supply store, where the drawing tools I favor are kept in locked cases. (Pretend my art is edgy.)
Montana white acrylic markers are a new favorite. I use them over other acrylics, which function as primer on absorbent papers, keeping the ink bold and on the painting surface. They are more saturated and opaque than white Sakura markers, and more versatile than the wonderful white Uniball Signo writing pens I use so often. And are refillable!