I generally use a local tool/hire shop for power tools, service cannot be bettered and they usually go to screwfix/ryobi direct ect on the web and beat the prices.
I just got some sealey stuff from them and they knocked quite a bit off the summer special deals prices and it was all here the next day.

As for fixings even the likes of newies can do screws at silly prices if you have a good relationship with them. (I spend a fortune with them though).

Being a trade customer helps even with screwfix/electrofix but most "PROPER" wholesalers can beat them on most items.

i normally buy from screwfix but i do like a wee wander into B&Q to see the offers

wouldn't have got my skil set at £25 from screwfix!! lol

I have to agree... Hiring is generally dead money, and although I will factor hiring of machinery into jobs, like you I prefer where possible buy an item then move it on again. There's then no deadlines or pressure to get the job done, and I still have an asset to sell at the end of it.

In respect of buying things, it largely depends on what you are talking about.

If its building materials, I use one local company for loose materials, as it works out cheaper than bulk bags, but if the site requires the need for bulk bags, then I use the phone to get the best price from merchants.

Timber wise, I have two 'contract' accounts, so in theory get a better discount rate than would be offered with just a normal 'trade' account.

Electrical tools, I use the Internet to source and would never use BnQ or Screwfix, as very often the tools aren't the same, as can be seen by the part numbers when cross referencing for price.

The only item that I buy from Screwfix, is stainless studding. I generally feel that everything else on offer is just market stall crap.