@tlester, here's what I do for your fist list:

- 15" Macbook Pro laptop

I leave my laptop at home and use a desktop at work.

- Charger (could leave at home... I have two)

You won't need this if you can use a desktop (or another laptop) at work.

- a few papers/journal

I don't carry any papers with me. Try to use online newssites, PDFs and other digital based media if available. Maybe scan them if they are important and have access to a scanner (and enough time)?

- A change of clothes (I typically wear shorts, t-shirt, underwear, socks, and tennis shoes to work).

Work clothing is one of the few things I do carry. But I leave the shoes at work.

- Gym towel

Can the gym provide their own towels? If not, then just leave it at work and carry it home on Fridays. Or maybe give it to a laundromat close to work on Friday?

- Shampoo, body wash, deodorant, comb

I just use the hand soap in the bathroom to clean up. Its mostly for my hair and face. Then just use some baby wipes as needed for the rest. Keep the wipes at work. Also keep an extra deoderant at work. I also keep a brush at work but rarely need it. Benefits of short hair cut and being follicly challenged. The #7 razor attachment is your friend here...

- gym lock

Leave it on the locker at the gym. Or if not allowed, then don't use the locker there. Keep your stuff in a desk drawer.

- Lunch/snacks

I usually buy lunch at work (we have a cafeteria downstairs). But you can carry a sandwich and some chips or whatever if you want to save money.

- iPhone

One of the other few things I carry in the backpack. Only other things are the few bike tools, mini-pump, and two tubes.