General:
* Writing implement
* Drawing tool
* Scribbler
More specific:
* Graphite pencil (if you want to emphasize the material)
* Lead pencil (a bit outdated but still used)
* Crayon (for coloring)
* Marker (for broader strokes)
* Pen (for ink-based writing)
Let me know if you have a specific situation in mind, and I can help you find the most fitting synonym!