I love it when the female cashier says "Do you need any help with your packing"
I immediately say "Are you being sexist? Just becuase I am a man, does not mean I am not capable of packing"
I have often been tempted to say that but have never had the nerve.

I prefer to use Waitrose where you get a handheld scanner to carry round the store as I can pack the bags as I go rather than at the checkout. Tesco are introducing scan as you shop in most of their larger stores now but Sainsbury's are going for self checkout in a big way.