Buy somebody a suspended coffee today with Social Bite.
What is a suspended coffee? You pay it forward and then a homeless person can redeem a cup of coffee. (And better than that you can buy them their Christmas dinner too.)
Pay in advance for a coffee or any item of food from their menu and a local homeless person can come into their shop to claim it. Text BITE00 £5 to 70070, or donate online through their JustGiving page.