There is no difference between the store brands and the national brands. However, there may be a difference between the stores. We have one grocery store in which the in-house brand has always been top quality (vegetables, etc). The other grocery store is quite a bit cheaper, but I find the quality is not there (discoloured vegetables, etc).
There are a number of companies that manufacture foodstuff and toiletries, then package them differently for the different contracts they hold. The same holds true for appliances also.
For foodstuffs, check labels carefully. Some of the cheaper in-house brands have more trans-fat added to them, so I would pay the extra for the better quality brand. Some cheaper brands also have more sodium. But, if the list of ingredients are the same, then go for it.
For shampoos, soaps, lotions, etc, it would all depend on what you like. I think that basically the formulas are the same, and it's just the scents that vary.
Do or don't do; there is no try (Yoda)