It is the first stage of the company's 'Make the Difference' scheme, which will be launched today.
For one day each month, Sainsbury's will run an event to encourage customers to take positive action and change across a range of environmental and ethical issues.
Next Friday (27 April), Sainsbury's will give away an estimated seven million re-usable 'Bags for Life', which usually cost 10p, for customers' shopping.
"We will provide the bags for free but need customers to re-use them to really make the difference," said Gwyn Burr, Sainsbury's customer director.
"Working together these small and easy changes today can make real and lasting differences for tomorrow.”