I clean storm drains (road dept)
Plastic bags are not an issue. Leaves and broken branches are number one, especially after a heatwave or in the fall of course. Water bottles are the biggest litter component by a country mile after leaves, dirt and gravel. 
That said, even though I return my bags to the store for recycling.

Water bottles are the number one form of plastic litter and street sweepers don't always get them because of the shape and light weight.
Just a FYI