I bought a $2 BART ticket and joined the queue. Fortunately, buses were appearing every five minutes or so. Looks like whoever managed AirBART actually realized that they needed more capacity and quickly. They had pressed into service some airport parking shuttles, which aren't ideal for this service because they don't have a front door, meaning the driver has to come back and take fares by hand, but it's better than stranding people at the BART station.
After around twenty minutes, I was able to squeeze into a bus, and shortly thereafter I was at the airport. Then I remembered that I'd forgotten to do online check-in, so I had to get in the regular check-in line for Alaska Airlines, rather than the short "web bag drop" line. I saw plenty of open self check-in stations, and nobody using them. I asked the eight or ten people ahead of me, "Do any of you plan to use the check-in stations there that are open?" and when they all said no, I asked if I could go ahead of them and use one, which they allowed as I could and let me go.
I expected a huge line for security, but they had four people checking boarding passes and all of the security lines open, with the result being that I had almost no wait at all. I made it out to my gate with plenty of time to wait. The airport was very crowded, of course, but I was able to find a place to sit down and read for a while before the plane arrived.
Because I'd put off making my travel plans, I'd had to buy a first-class ticket, which fortunately was only expensive, not impossibly expensive. You don't get much extra in first class on such a short flight other than early boarding and a bigger seat, but it was still nice enough. We were slightly delayed because it took so long to load all of the luggage people were bringing, but otherwise it was an uneventful flight to Portland. After claiming my bag, I hopped onto light rail and rode over to Parkrose/Sumner, where Lisa was waiting for me. An advantage of traveling on a later flight than usual was that traffic wasn't so bad, and we got out of Portland and headed south, after stopping for dinner at the T/A truckstop (because they have pinball machines we like to play).