Some products are harder to produce under the same conditions as others. Chocolate-based ones each have very specific production methods that are nigh impossible to replicate properly. Soda brands each have their own formulas that they keep on lock-down. Things like potato chips and cereal, however, are easy to make and as a result easy to replicate because of their basic preparation methods. Generic brands are on a closer level to those name brands than to the name brands of other, more complex products.

I frequently eat Great Value stuff, which, unsurprisingly, tastes like complete and utter [censored]. You get what you pay for.

Food usually tastes the same or something close to the same. Drinks usually taste noticeably different.