Supermarket chains in the UK actually have product lines, which are referred to as
Loss Leaders . They actually market and sell them at below wholesale prices to entice customers into the store. Once they get the customers into the store then the rip offs and the supermarket profits can begin.
One of the major supermarkets we have in the UK has a Tag line 'Helping you spend less every day' and 'Every little helps', which is obviously ridiculous from the standpoint of the supermarket chain.
Identify the national supermarket chain loss leaders (which may vary from week to week etc) for each supermarket chain and you can potentially save lots of money on those lines, even if those lines were purchased from a wholesale source. You can get the rest from Wholesale sources. Many Wholesalers will normally require you to open up a business account but many may operate a day account with minimum spend policy. i.e. you have to spend a minimum of $100-200. This can be a good way to save cash (i.e. 30-40% retail mark tup) when purchasing long life tinned goods for the stock pile. (A visit to the wholesaler will also help you identify the supermarket chain loss leaders)
Fresh produce is then best bought from locally based retailers, town and farmers markets, where substantial savings can be made over national supermarket chain fresh produce.
Supermarket chains use a lot of psychology in the way their stores are designed and laid out. Get to know the rules of sales and marketing psychology the supermarkets employ and substantial savings can be made.
Never go shopping when hungry and always have prepared list after doing a little research (comparative costing from other sources i.e. a comparison database on a Palm handheld for example)
Internet shopping from national supermarket chains can be useful despite the carriage charges. It allows you to shop with much less psychological pressure and the rolling bill can be very useful to keep within budget.
Most of the time the delivery charges can be recouped anyway. On most occasions the supermarket will not be able to completely fulfill the Internet shopping list. Many supermarket Internet retailers will drop the delivery charges if you complain if any of the ordered lines are missing. Plus of course you have saved time and effort and annoyance and the cost of the petrol and mileage depreciation on your vehicle.