Antique Powerland Museums located in Brooks, about 15 miles south of the park. They have an exceptional truck museum ($5) that initially attracted my attention. The collection ranges the gamut from hard rubber, chain drive trucks to nearly new prototypes.
Great Oregon Steam-Up. ($10)
Evergreen Aviation & Space Museum houses the Hughes "Spruce Goose" and many other quality exhibits. They have especially strong collections of helicopters and military aircraft.
(By the way, further afield in Tillamook, Oregon is another very interesting aviation museum. Smaller collection, oil drip pans under each engine with all aircraft in the collection being fully operational.)
Red Hills Market one block off the main road in Dundee. It's just 8.5 miles from the park and much closer if you're a crow. Wood fired pizzas, wonderful sandwiches, special salads, etc. It was excellent. Fair warning - the parking lots were jammed early Saturday afternoon.