I'm American and that's what I would say for "a couple". "As few" to me is just a small amount compared what is typical. So a few marshmallows might be 2 because generally people have somewhere between 5 and 10. A few skittles might be 5 because people will take a handful normally which is 20 or so skittles. "Several" to me is "a little less than the average amount" so with our previous example 5 marshmallows, 10 skittles.

I'd bet that most people have this kind of relative meaning for these words