Hotel reservations. It's always a good idea to book early in Seattle. While the high season and major events require advanced reservations, even random low season weeks can be choked with visitors for conferences and business conventions. This extends to B&Bs and even past city limits—accommodations go fast (including campsites) on the San Juan Islands, Mt. Rainier, and the Olympic Peninsula. Waterfront or water-view hotels, like the Edgewater and the Inn at the Market, see their best rooms booked six months in advance.
Restaurant reservations. Seattle's latest (and certainly not greatest) dining trend is the two-hour wait at places that don't take reservations. It never hurts to ask if you can reserve, and you should definitely lock down your table at splurge restaurants (most of which do offer reservations). If you have a large party, a reservation is even more important and may be easier to come by.
Tickets. Nearly any act that makes it to Key Arena is going to sell out. National touring acts at smaller clubs like Neumos, Showbox, Triple Door, and the Crocodile also play to full houses. Tickets for the most buzzed-about movies at the Seattle International Film Festival should be purchased as soon as they go on sale. Visits to the Bloedel Reserve on Bainbridge Island are by appointment only, and booking well in advance on summer weekends is advised. Tickets for major-league sports—such as Sounders and Mariners games—should be booked online in advance.
Car rentals. Though the parking lot that is Interstate 5 (I–5) may suggest otherwise, quite a few Seattleites don't own cars. On summer weekends, you'll be competing not only with the thousands of other visitors in town but also with residents making an exodus toward the mountains. If you find a good rate, book it immediately, especially at the few downtown rental offices. (Remember: you'll find better rates—and no airport tax—if you book in town.)
Train tickets. Amtrak tickets to Portland and Vancouver, B.C. sell out on summer weekends, and last-minute fares can be quite expensive.
Ferries. Whale-watching/ferry ride vacation packages like those offered by the Victoria Clipper can be booked in advance. The Washington State Ferries rarely accepts reservations (only on international sailings to Sidney, British Columbia, for example), so be sure to plan island travel thoughtfully: leave enough time in your schedule to arrive at the piers early—and to wait for the next ferry if you're last in line.