2.1. Undo  Ctrl+Z

Undo the last action

2.2. Cut  Ctrl+X

Cut the selected object or group and put it on the Clipboard

2.3. Copy  Ctrl+C

Copy the selected object or group and put it on the Clipboard

2.4. Paste  Ctrl+V

Insert the object or group on the Clipboard

2.5. Paste Mirrored  Ctrl+L

Paste a mirrored copy from the clipboard.
The pasted object is mirrored about the centreline of the front view.

2.6. Deselect  SPACE

Deselect the active selected curve, mask or object.

2.7. Select Previous  PageUp

Cycle through the objects in the scene.

2.8. Select Next  PageDown

Cycle through the objects in the scene in reverse order.

2.9. Delete  Delete

Delete the current masked region, curve, or objects.

2.10. Toggle Tool Add/Sub  \

Swap between opposite versions of related brushes.
Handy when sculpting with a tablet and you don't have easy access to the right mouse button.

2.11. Mirror Sculpt Brushes

Turn on to sculpt on left & right side of your model at once. Duplicates the effect of sculpt tools to both sides of your model.

2.12. Auto Polish

Smooths and evens out the mesh as you sculpt. Very helpful when sculpting an Adaptive Subdivision Mesh. You might want to turn this off to get a crisper result with Noise and Pinch sculpting tools.

2.13. Auto Divide

Turn on to use Automatic Subdivision while sculpting to add mesh detail where needed.

N.B. Requires an ASMesh and is not active when sculpting a regular Mesh.
You can tell which kind of mesh you have by looking at the bottom right of the viewport, and can convert to ASMesh by pressing J.