Not really a self sufficiency post but it's helpful in today financial climate.
Clubcards are irritating and intrusive, BUT they do serve one good purpose, they give you something back (in addition to your shopping naturally).
Take the Tesco clubcard for example, discreet enough on a keychain or in your bag (they come with a normal credit card sized one and a couple of smaller ones), if used regularily enough can also accumulate a fair value that you are sent every quarter in the form of vouchers off products.
This is good

fractionally reclaiming money to put toward subsidising future shopping trips. Some people dislike the idea that their purchasing choices are being stored, however its my experience that the voucher you are sent are for the products you buy most commonly.
Its worth getting just to save a bit of cash, in Urban Survival just like Tesco every little helps.