I prefer packing them myself and always say "no" if asked if I want any help. It's just so much quicker that way. Only time I appreciated help was when dd2 was tiny and screaming and I had to rock her while they packed my bags for me.
Today at Asda the woman at the checkout just started packing for me without asking, and then I'm too shy to say "I'll do it myself, thanks." So I let her do it, but it was soooooo slow. When she started to get one of those small plastic bags to wrap the already wrapped cheese and the I can't believe it's not butter before putting them into a bigger bag I had to stop her. They always seem to put so little items per bag, and do extra wrapping with little plastic bags, I mean what is the point? Madness, if you ask me.
Just had to get that off my chest.