Couple of things that spring to mind when reading the recent responses above;
1. Electronics with lithium batteries cannot go in the hold due to fire risks. Almost eveyone carries at least one these days. This needs to be factored in when people carry one cabin bag with everything in it.
2. I'm one of those people with two bags. I (or my company) pay for the privelidge. 1x size compliant case and a bag of all my electronics (for under the seat in front). Given that I pay my way; it is somewhat infuriating to see people bring onboard 1 huge bag that takes more space than my 2 and they didn't pay a penny.
If you come across a pax with oversized bag it takes a good 5-10 mins to get the £/€50 payment especially if paying by card.
3. Simple solution, "sir/madam your bag does not comply with the rules. Please join the end of the queue and we will deal with it when everyone else is processed". If they miss their flight as a result, it's their own fault for not complying with the rules.