Alaska is not a place you drop into for a weekend and tick off. Anchorage is the biggest city in the state and the entry point for almost everyone, and the road south from it is the most useful 127 miles in the country if you want mountains, glaciers, whales and bears without chartering a bush plane. Seward sits at the end of that road on Resurrection Bay, and the town is named after the Secretary of State who arranged the purchase of Alaska from Russia in 1867. The highway between the two follows Turnagain Arm, a tidal inlet with huge tide swings, and ends beside Kenai Fjords National Park, where glaciers pour off the Harding Icefield into the sea.
Be clear about the season before you plan anything. This guide is for summer, roughly mid-May to mid-September. That's when the Kenai Fjords boats run in full, the Coastal Classic train runs, the Exit Glacier road is open to cars and the days are up to 19 hours long. In winter much of this plan stops existing, and the northern lights belong to the 3 Days in Fairbanks guide. Five days is the honest minimum for this route. It gives you a day in Anchorage, a day on Turnagain Arm and in Girdwood and Whittier, a day for Exit Glacier, a full day on the water, and a slow drive back through Cooper Landing. Denali is not in the plan: it's about 240 miles from Anchorage, and it needs its own two or three days.
The plan runs Monday to Friday: Anchorage on Monday, Turnagain Arm, Girdwood and Whittier on Tuesday, Exit Glacier and the Harding Icefield Trail on Wednesday, the Kenai Fjords cruise on Thursday and Cooper Landing and the way back on Friday. Start on a Monday. The Seward end of the highway is a weekend escape for Anchorage, so the Exit Glacier lot and the harbor are quietest on weekdays, and Seward also fills with cruise passengers on ship days, which you can't dodge but can plan around. Avoid the July 4 weekend if you can, when the town hosts the Mount Marathon Race. Details on travel in the country are on the United States page.