This was one story in a paperback collection of three stories, all by the same author I believe. The collection was titled "Three Tales of the Wolf".
In the post-apocalypse story, the desert-dwelling survivor kills a courier delivering desperately-needed vaccines to a high-tech enclave.
In the second story, people start wearing prosthetic memory devices called 'Ticklers' that manage their schedule, send messages, and give them an advantage in business. The Ticklers become sentient and begin using their humans as hosts. The hero persuades the Ticklers that Earth is too small for their ambitions, so they build a spaceship and abandon the human race.
In the third story, pressures building up in the human race cause increasing violence and suicides. Governments respond by inventing an alien threat and moving the economy to a war manufacturing footing.