I have both pack rat and weight weenie tendencies.

So I ride a basic 20 lb road bike and carry a backpack that has at least 2 lbs of stuff in it that has no reason to be there.

I am a little surprised at some of the advice. Personally I HAVE had 2 flats in one ride and was thankful to have both a spare tube and a patch kit. Not only that I was able to help somebody else out a couple a weeks ago who had a flat. I happened to have an extra (partially used) patch kit on my bike and just gave it to them. It's not like those things weigh a ton anyway.

It's also worth it to me to carry a lock vs leaving it at the office. What if I need to stop somewhere between home and work?

The bottom line is that if you're not bothered by 50 lbs worth of bike and accessories then that's all that matters. It's your commute. If it's 100+ degrees outside and you feel it's wise to carry a couple extra bottles of water then do so. To me there's a certain convenience and fun involved in having a light rig but it's an entirely personal choice.