Here in Seattle, I'd suggest something like this:
Activities -
Tour Pike Place Market, right as it opens to beat the crowds. See the first Starbucks (it's not really the first), find the memorial to interned Japanese-Americans and the gum wall
Walk the Olympic Sculpture Garden and the old waterfront
Do a Ride the Duck tour or Kenmore Air Seaplane tour
Visit Kerry Park
Rent Kayaks at Agua Verde in the U-District or Kayaks or Bicycles near Marination Ma Kai in West Seattle
Go to a Sounders match, Seahawks, Huskies or Mariners Game depending on the season
See an IMAX film at the Pacific Science Center
Museums are plentiful, but there are many, so that's more to individual tastes
Visit Kubota gardens
Outside the city -
Boeing 777/747/787 Factory Tour,
Hike to Rattlesnake Ledge or Snow Lake, or
visit a micro distillery and winery
Food -
There are food options from Ethiopia to Oaxaca represented in big American cities, so this list is only a start.
Use Yelp.com or their smartphone app to "explore the menu" to help you decide what to order:
Breakfast at Portage Bay or a similar upscale/organic breakfast restaurant
Dim Sum (the International District)
Thai Food (the Ave/University District)
Food and a tasting at one of the Elysian pubs
Fish and Chips, or other fast food, but try tarter sauce on your fries
Try a Seattle-style hot dog
Sushi
Day/multi-day excursions -
Mt Rainier National Park,
Lake Chelan/Leavenworth,
Olympic National Park,
Mt St Helens,
Portland,
Hood River,
Mt Hood/Timberline Lodge,
San Juans or Victoria, BC,
Vancouver and/or
Whistler