CASH IN THOSE CREDIT-CARD MILES and you're financially halfway to wading among millions of salmon along the Parks Highway in southern Alaska. Fly to Anchorage the last week of August, rent a car, and head north for great river hopping along a 70-mile stretch of the Parks (a.k.a. State Route 3). Bring light camping gear, lots of flies, and an extra rod to replace the one you'll likely shatter. There will be silvers, chums, sockeyes, humpies, a late king or two, and the errant rainbow.