Checkout Consumerium services wherein you just grab the GTIN codes as a form of realised shopping list to download to your home computer to retrospect on purchases is the most important function at the Checkout counter. This could be done optimally via NFC or alternatively Bluetooth.
It is typically the point of sale, that is, where money is exchanged for goods.
It is also a main marketing point where information is presented by "checkout TV", supermarket tabloids, fashion magazines, impulse buys such as chocolate bars, and other high profit items that people don't need, but can sometimes buy if they're in line long enough.
Worn devices can be used at the checkout counter much as at the retail shelf. The checkout wait may be an ideal time to review your purchases with the Consumerium buying signal, especially if you are over-spending already and seek to return some non-essential items. This is easier if there is a bin to stash the items you're refusing to buy. Seeing many of the same item unpurchased, and requiring return to the store shelves, may be a much stronger signal than simply not taking it from the shelf.