Trolleyology

This is an American term describing the ways that supermarkets get you to spend more money. From the simple things such as placing things at eye-level, to putting everyday goods (such as bread and milk) at the back of the store, so that the customer has to walk past more profitable goods, they've got you as soon as you walk in. This is explained in more detail on the 4 Money site and in this Allsands article.

There's some crafty additional techniques though; like putting a central aisle up the length of the shop - this means they double their aisle ends, and these are where all the targetted high volume goods are. There are two golden rules to surviving the post-Christmas sales: never shop on an empty stomach and never shop on an empty head. Concentration is key. See this Telegraph article for more of the same (via JWalk).

And in case you though this was just marketeering, there's obviously some science behind this - read some of the studies and watch some videos at the University of Illinois' Food and Brand Lab, particularly the experiment with Soup signs ("How signs make you buy more"). The BBC have their own take on it in this video.