Small rucksack (Newtown St Boswells TD6)

I think the 'Run Commuter' site says it all:

'This small, light backpack is simple yet sturdy and is perfect for a certain type of runcommuter. It is about as basic as you can get in a pack designed specifically for running/sports. The Speedlite 10 is a great runcommuting pack for those who value durability, quality, and simplicity, but more significantly, those who want a pack that they can forget about while running...'

Of course, I never used it for running, sedate walking is more my style... It will comfortably hold everything needed for a short walk - lunch, phone, sweater, slim water bottle and whatever else you can cram in.