I usually use the self check out line at the grocery store. I like it. I use my own bags from home, and they are at the bottom of the cart, so, I can't start bagging until I finish ringing.
The next customer standing too close and generally exhibiting impatient behavior brings out my passive aggressive side in a big way. I mean, I can pack those bags just so slowly that it would blow you away. The dry foods go in one bag, the fruits in another, and so on, you get the idea. There is the divider that comes out so I can separate my order. If the person behind me is behaving in an impatient manner, I don't bring out that divider until I'm Just about done bagging, but, I am sure to bring it out, because, if I do, the next person will have to come down and put it away to bag their order. Then I smile my sweetest smile and say "it's all yours!"
One woman particularly galled me. I was bagging my order, standing between my cart and the checkout counter. I can't reach all the way to bag my order if I stand at the end. She sent her child around to get bags ready for her order, and wanted me to move to do so. Well, I am very petite, and there is almost enough room for a child to pass even with me, my cart and the child in the lane. But, I told mama that I wasn't done yet, and could she please wait until I was done before sending her child to the end of the lane. Of course, that day, I didn a fabulous job of meticulously bagging my groceries, taking at least three times longer to do so than normal, and putting out that divider just as I was finishing up my last bag.