There are many reasonable suggestions within this thread. However, I don't see any remotely multimodal options. Ortlieb's offerings are the best I have sampled and I would continue to rate them as a slight movement in the right direction.

This was my day (and a reason that I won't change away from a backpack.)

I cycled into work with a 20L backpack with a MBP, bike lock, phone, lights, passport/wallet.

Stopped at the barber for a beardtrim/headshave and locked the bike to bike post (couldn't leave anything in panniers outside.)

Then, I rolled over to a coffee shop for a take away.

Then, arrived at work and locked it outside the office in the bike rack.

My partner called and said the weather is nice, so let's go to Winchester with our new daughter. I said great and bring my dSLR as the extended family is going as well.

They met us at the local mall so we could go to the bank and open a child ISA and hit TK Maxx.

They we hoped in the car and drove 30 miles to Winchester where I pushed the daughter/pram around.

It was around 5 miles of walking and sme shopping and some coffees/cakes.

Then they dropped me off at the uni, where I hopped on the bike and rode home.

Over the course of the day, the backpack had:

To barber (lights, passport/wallet, bike, lock, MBP, phone, etc...)
Locked on corner near coffee shop (same but lock)
Bike rack (same but lock, left stuff in office not needed)
Walked over to mall (phone, passport/wallet)
Added (dSLR, ID documents for daughter)
After bank (dSLR, passport/wallet)
While pushing pram (partners jacket, shopping, dSLR, ID)
At office (dSLR/MBP/bike lock/etc)
Cycle home

I don't see panniers with the same utility.

This is not an abnormal day by any means and just had a personal car as the second mode instead of train/bus/hovercraft/plane/taxi.

I don't see how a backpack can be beat for sheer utility.

Perhaps we have different lifestyles / living environments.