I've earned £3000 so far from Topcashback/Quidco/Reward Gateway. I earn £300 cashback a year by getting my SIM through Mobiles.co.uk + TCB. I earn hundreds by switching bank accounts, and moving money around 10 different bank accounts so I can get the monthly transfer bonus. I have a Barclaycard Reward for zero international transaction fees when abroad. Some cards have cashback on purchases. I have bonds with NSI, which is basically a free lottery ticket every month, earning over £1000 a month best case. I use Compare the Market to find me the lowest insurance every year rather than stick with the same plan. I use Zen Internet because they are super reliable and it's a fixed price forever. I use Vodafone because from tests and Ofcom charts, they have the best signal - though their customer service is not the best. Vodafone also have VeryMe (similar to O2 Priority) with ocassional freebies. I don't use Trainline because you don't get charged fees if you order direct, typically a ticket is valid for any operator, and their refund feature undermines better compensation via Delay Repay. Loyalty cards and reduced section can be a godsend. More advice on Money Saving Expert (by Martin Lewis), and good offers on HotUKDeals.
