Ask Costa to start allowing 'pending coffees'.
A caffè sospeso Italian for "suspended coffee", or pending coffee is a cup of coffee paid for in advance as an anonymous act of charity. Go in for a coffee and buy two, one for you, one pending ... A poor or homeless person enquiring later whether there was a pending coffee available would then be served a coffee for free, as you paid for it earlier.
This petition is aimed at Costa. Who have 2, 422 stores in the UK alone as of 2019 (https://www.statista.com/statistics/283302/number-...)
In 2017 the number of people sleeping rough in the UK was near 5,000 (https://www.homeless.org.uk/facts/homelessness-in-...)
Your signature here may help persuade Costa to implement 'The Pending Coffee' and allow the thousands of people who buy coffee from Costa every day, if they wish, to pay for a coffee or meal in anticipation for others who can't.