In a halachically public area (reshut ha'rabim) with no eruv, on Shabbat you may move a stationary object up to 4 amot (6'9 1/2", or about 2 meters) from the place where you find it. If you are already transporting the object when you realize it, do whichever one of the following applies:
Situation You are walking on Shabbat in a public domain (reshut ha'rabim) that does not have an eruv and find something in your pocket.
What To Do

• If you were walking and are still walking, go back to the most recent private domain and leave the item there. (If you cannot reasonably get back to where that was, continue to your destination and drop the item inside the first private domain you reach.)
• If you have already stopped walking, drop the item where you are.
• If you had stopped walking and then resumed walking, drop the item where you are.