Geocaching rocks (Swag tutorial)
Inspired by Doodlestones I've started making georocks.
Fast to make, not expensive and fun to find as swag for geocaching.
Short tutorial for drawing or painting on rocks.
Painting with brushes takes some time. Working with markers is fast.

Stones
Depending where you live you can find them at the beach, moutains or near rivers.
Nothing in your neighbourhood?
Have a look at a garden shop.