Your friend is wrong. It is generally more accurate to say that all contracts for the purchase of Goods or Services have no cooling off period
except in certain cases, such as distance selling and unsolicited callers to your home.
A comprehensive list of the exceptions can be viewed here...
http://www.consumerdirect.gov.uk/your-rights/f s_c01.shtml
The 'various extras' you mention will form part of the contract between you and the shop, and failure to supply them would be a breach of that contract. However, if they were not part of the
written contract it would be difficult for you to prove that their existence was a condition of the agreement you signed.