I aim for a 20-35 l bag

I keep seeing you tubers displaying their GHB and BoB's full of wilderness survival equipment -- and they live i the middle of a city...

What´s the difference between city and wilderness if you can´t get into a building in the city?

I see teacher's point. The environment that I am preparing to travel through should dictate what I do and don't carry. The mission will also effect my kit content.

Where I am going, what I am doing, who I am with and how long I expect to be out all effect what I bring and how I carry it.

If you have the items useful in a wilderness setting (fire, sleep, shelter, water, and food) you are set for anywhere. I live in a full on urban environment and the wild woods are within easy walking distance.

I also pack gear useful in cities -cash, credit cards, means of self defense (rarely)

Also, in some cities you might (or might not) be smart to find a park to camp in during a crisis. Options are good.

Things which are very useful in the city, but not in the wilderness
a bus schedule
credit card
phone charger
silcock key
ID
uber account

Actually a phon charger can be useful in a wilderness setting as well lots of relevant apps for a phone (Gaia, etc)

For sure, I have off-line maps in my phone.

I was thinking of one that plugs into the wall