Breakfreefromplastic.org has some useful bits and pieces on plastic use, which could be helpful for market failure topics. There is a brand audit report which is handy but also a good source of discussion on methodology, as the "10 Worst Polluters" is based on physical waste found - I'm sure your classes might have some ideas on whether that is a good measure. Rankings like this are useful for 'higher or lower' activities, 'put these in order' or just 'how many of the top can you name?'.
