[MSL]

 Shopping cart (US), buggy (US, Canada), shopping trolley (UK), trolley (UK, South Africa, Australia).

^{By Jim - http://www.flickr.com/photos/alphageek/121953651, CC BY-SA 2.0, https://commons.wikimedia.org/w/index.php?curid=1103173}

[mojo]

The shopping cars in the image are of the standard size. Most of them come with a fold down seat on the inside where you can put a child and his/her legs will stick out towards the shopper. There is another size smaller. Mainly used in stores where floor space is at a premium and the displays are closer together. A full size cart would not get between the isles.

In many places the expectation of the shopper is to get one at the door, do their shopping while the cart contains all the products, go through the cash register where items will be bagged and put back in the cart, and then the shopper takes the cart to their vehicle. They unload it and most of the larger stores have a buggy rack where you leave them. Often people are lazy and will not bother with taking them to the buggy rack and just leave them in place where they are in the way for the next customer to park their car. Usually these places have folk who's job is to go round up the carts and bring them back to the store front.

In an effort to cut down on the labor of having to have some one go get the carts, some places charge a nominal fee, such as a quarter to get a cart. You put the quarter in a coin slot that is part of the buggy. The buggy then unlocks and you are free to use it. To get your quarter back, you must take the cart back to the place you got it and when you put it in the rack, your quarter is released back to you. 

[mojo]

Something I thought of after posting this as a bit of trivia, is that when the shopping cart was first invented and saw it's first uses in stores, the customers did not want to use them. The inventor had to hire people to push them around in the store to show their usefulness before they became accepted.