Not "the best beers" — the beers that let you run the flights the course is built on. Each purchase below maps to a specific lesson: the two hop axes, the ale/lager fork, the roast, the freshness clock. Gather the core four, and Session 19 (comparative tasting) does the teaching for you.
One trip covers the whole spine of the course. Grab these four, all as fresh as you can, plus one glass:
That's three flights and the serving lever from a single visit. Everything else on this list widens the map — buy it as the sessions call for it.