Levels of Distractibility: Who cares? = *. Some people will be distracted from your meaning: = **. Many people will be distracted from your meaning: = ***.
Question: When should you use "fewer" and when should you use "less" ?
Answer: Use "fewer" with things you can count as in "fewer people." People who say "less people" should be....
Use "less" with things you can't count: "less money." BUT: "They have fewer dollars to spend."
How do you avoid the supermarket usage, "two items or less"? You can't. "Fewer" not only has two syllables, it sounds uppity, prissy. You could say, "Customers are limited to two items." But supermarket managers are not going to waste time trying to use correct English. Besides, when the English is incorrect, people notice the item and for the supermarket, that's good.
Some day, I'm guessing, the battle between "fewer" and "less" will result in "less" being used for both. The English language always moves toward simplification. Whenever usage requires too much thought, one usage will take over exclusively and the other will be dropped by the wayside. That's what happened to "You," "thou," and "thee."
Rating of Distractibility: ***. This usage gets the "Scratch Nails on the Blackboard" award for one of the most egregious errors in English.