Post it notes for masking
The familiar little squares in a sticky tablet, are the greatest addition to a drawing table tool kit. I use them to mask out, create edges, and make safe places to set my dirty hands on. I also use them with the kneaded eraser (and plastic eraser) to shield out areas I wish to protect. Used with almost any media they will protect areas from spoil, they lift off without leaving any noticeable residue, are re-useable, inexpensive, and you can shape them.
If you get white ones as well as colored ones, you can see through them enough to trace outlines then cut a mask to fit your needs.
If you use them with graphite though, they will lift some of the graphite if you stick them to it, use them only on un-rendered paper.
With ink you can use them over the ink without any problems.
I keep a sharp pointed pair of Scherenschnitte scissors, and an x-acto knife, nearby, to cut into the sticky edge side. Also a hole puncher to nibble out edges.
Use with Graphite shading, pastel, pencil cross hatching, ink line hatching, finger smudging effects.
The list is huge. Go buy some and use them beside your drawing board.