I live opposite a Greggs and most people who buy a pasty or a sausage roll there do the following.
1. Leave shop with item in a paper bag.
2. Eat item while crossing road.
3. Throw away the paper bag on pavement.
Why do Greggs not ask them whether they would prefer to just have the sausage roll or pasty in their hand. It would save Greggs money on using less paper bags and it would stop the street being covered in rubbish.