Salt brings out flavour, and stops baked goods from getting too sweet. Pepper makes things...taste like pepper.
I tend to cook without salt if I can help it. I hate it when food gets too salty, and I find that if you cook with nice food, the flavours speak for themselves.
If I do want to make a flavour base for cooking almost anything, however, you can't go past onions sauteed in butter - here's the part that's relevant to this post: in NZ, all 'normal' butter is slightly salted! It's what I grew up with, though, so I find that the saltiness level of Anchor Butter is about the saltiness level I want in my dinner.
French fries are an exception ;-)