My LHBS sells a packet of "Burtonizing Salts". Will it be equal to Burton on Trent water? Not likely, unless the starting point is the same. The LHBS uses its local water profile, but the town that is a couple towns over has notoriously bad brewing water and the next town over has remarkably good brewing water to start with for most recipes (a small Belgian style microbrewery located there for this reason). I brew with RO as a starting point.
We are all assuming an all grain approach, also, because extract already has the minerals in it that were present in the water used to make it.
I agree with most comments above. If you guys are looking for a silver bullet of salts, there is none (despite a product that is sold to get your pH to be 5.2 "spot on" regardless of starting point.) Thankfully, the grain does most of the work here and the additions that are suggested are typically very minimal amounts (in the single digit gram level of weight for most of additions of salts and acids/alkalines for the beers I brew - and that is a ten gallon batch!)
Don't fall victim to the 1 teaspoon of CaCl for malty beers and 1 teaspoon of CaSO4 for hoppy beers. It may be that those are correct for your water, but without knowing where you are starting, there is no way to predict where you will end up.
Martin has an advanced degree for a reason. The stuff just isn't that simple.