Collingwood Recreation Ground is a great family friendly park space in Sutton with an enclosed playground, basketball court, skate park and static exercise machine area, not to mention a large open field surrounded by trees.
The Recreation Ground is situated adjacent to Sutton United FC's home stadium, The Borough Sports Ground, and there are often footballers to be seen playing on the football pitches marked out in the park during the football season.
There are always plenty of dog walkers about so some stealth may be needed, although I've endeavoured to find a fairly quiet spot away from the busiest areas of the park.
You are looking for a small black container, slightly larger than a regular nano but not by much. No space for anything other than the tightly rolled log sheet (please be sure to roll up tightly using the included makeshift roller so that it fits back in snugly!) so please bring your own pen/pencil.