I couldn't agree more. We are trying to do the same with our puppy. Everything that I can think of.You want to ensure you socialize him with dogs AND people (kids, elderly, wheelchairs, scooters, skateboards, bikes, etc.), sounds (trains, cars, bangs, booms, metal dropping, babies crying, kids yelling, people singing, etc.), objects (anything and everything you see, let your puppy explore it), places (go to as many places as possible, make sure to mix it up!), different surfaces (metal, plastic, paper, carpet, hardwood, grass, ashfault, dirt, sand, pebble, water, rock, etc.), different heights (on top of tables, under things, etc.), the list is endless.
Even at 18 months old my boy is still being socialized daily to all these things.
We sometimes dog-sit a friend's lab and have noticed that since they didn't socialize their dog well..small things set her off. eg: each time she sees someone walk/jog by with a headphone stuck to their ear..she will lunge !!!