Grocery Store Etiquette...

When you are walking down the isle doing your grocery shopping, what do you do when you run into other people, strangers?...do you avoid eye contact even though you are keenly aware of them around you? What about when you are walking down a longer stretch where you can see a good 100 feet in front of you… as you are walking forward, do you pretend to be looking for something? What do you do when you notice a couple other people noticing you? And if you are the one noticing them, what kind of reaction to anticipate?...and finally, do you look at other people’s grocery carts and notice what they are buying and make judgements there in? Why do people stand so close in line, almost touching? WHAT IS PROPER GROCERY STORE ETIQUETTE???