Pattern index
The twenty recurring ideas that solve most of these 31 problems, each with the problems where it appears and the sentence that earns credit for it.
Numbers cheat sheet
Latency constants, capacity rules of thumb, storage and bandwidth arithmetic, and the specific figures from these 31 designs that make an estimate credible.
Tool selection
Which datastore, queue, stream processor, and cache to name, what each one is actually good at, and the boring choice that is usually right.