All you need is a sketch pad and several pencils with hard and soft lead, and an eraser.

Sketch Pad...Any size you feel comfortable with.
"H" on art pencils means "Hard" Good for sharp details.
"B" on art pencils means the lead is soft. Soft lead is good for smudging and shading.
2B is soft ...9B is softer.
Kneadable eraser. A real must. It's soft and pliable.
The hard rubber eraser can ruff up the surface of the paper and ruin it..
smudge stick, or your finger....or a or cotton q-tips work pretty well.