Fixative:
I spray all my drawings with a fixative. It provides a protective layer, preserves the art and prevents smudging.
Sharpener:
A good sharpener saves a lot of nerves. If pencils break often, it may be due to a dull sharpener. I use a manual pencil sharpener but also a handheld metal sharpener can perform well.
Additional tools:
Sandpaper (to clean blending stumps), a utility knife to cut paper and rulers are also useful.