Some of us keep a pebble in our pocket, a beautiful pebble we picked up in the front yard. We washed it very carefully and always carry it with us. Every time we put our hands in our pocket, we touch the small pebble, and hold it gently. We practice mindful breathing and we feel very peaceful. When anger arises, the pebble becomes the dharma. [...] Just holding the pebble, breathing in and out calmly and smiling, can help you tremendously. It sounds a little bit childish, but this practice is very useful. When you are in school, at work, or out shopping, you have no reminders to bring you back to yourself. So the little pebble in your pocket serves as your teacher, as your fellow practitioner—it is a bell of mindfulness, allowing you to pause and return to your breathing.
[...] It can help keep enlightenment alive in you.
Source: Anger (2001) by Thich Nhat Hanh; Ch. 3.