I'm seeing the appeal of a daily carry sling bag.
Big enough to carry a book, mask, snack, etc.


*One strap bag, man bag, purse, etc.

A sling bag is great if you keep it small and light. A larger bag invites overpacking which is not good one one strap. I have a Maxpedition Kodiak Gearslinger which I pressed into service as a laptop & book bag for college and it was miserable. It's a good sized pack, maybe 25 liters, with a single strap that's fairly thin for the size of the pack. Loaded up with a computer and books for three or four classes it was excruciating to carry.

Many years later I bought a really cool sling bag from Hazard 4 called the Rocket pack. I loved the looks and the format (a sling bag tall and narrow with zippered bottle pouches on either side). Very cool on paper but in practice not as good as I'd hoped. It's around 20 liters with one strap but the strap is very very wide and well padded. Much more comfortable than the Kodiac but the problems still remain, more of balance than comfort. A sling pack doesn't really carry as well as a pack with two straps (and perhaps a waist belt). To carry in the car it works very well, and as a pack that will mostly ride along and maybe be carried from the car to a site or even carried a ways on level ground it's okay. But it fails as a technical pack and doesn't carry well if you carry it on a hike.

To me the "killer app" for a sling bag is as urban EDC or even a wilderness PSK if kept compact. My latest experiments have been moving my large sling PSK contents to a Mystery Ranch 2DAP and working up a smaller PSK in a Maxpedition Jumbo Versipak or GTG bag.

I have a Patagonia Atom Sling which is empty until needed and is only loaded with immediate needs. I take it on my urban walks to carry basic needs while minimizing unnecessary weight. Your thoughts as to use as “urban EDC or even a wilderness PSK“ are on target.

It's definitely doable, but like Phaedrus said, you've really got to be disciplined and keep it light. Your list of what you anticipate carrying seems fine.

I tried it a few times, just because I thought they were pretty cool on paper, but when the rubber met the road I found it was super easy to overpack and I was missing a backpack.

My progression went like this:

1. Get Nalgene bottle pouch for a minimal way to carry some water on a dayhike.
2. Add some additional pouches, but then it was a bit ungainly and starting to feel the weight
3. End up buying a Jumbo Versipack which has great organization and does all the things I was trying to do with the condor + pouches, but was a little more ergonomic with a wider strap
4. Overload it
5. Wish I had a backpack cause now it's not all that comfortable
6. Buy a Maxpedition Sitka knockoff sling-bag because it was pretty cool
7. Overload it
8. Wish I had a Sitka style bag, but with two straps...
9. Get Vanquest Trident 20...
10. Overload it

(I have a problem! lol)

I know you're not looking for a full on backpack since you were thinking EDC. I'd say if you can keep it under 6 pounds with a single thin strap, or under 12 pounds with a single wide strap you're okay. With two straps, 20-24 lbs. Anything more is doable short distance but would be annoying for any real period of time. Beyond ~25-28 pounds I'd really want a pack with a proper load bearing hip belt if I were going any distance.

I went through Chicago airport once with a duffel instead of a backpack. Never again!

What benefit would a sling bag offer over a small backpack/daypack?

Lets your back breathe. You can get something from the bag without taking it off. That´s the main thing to me.

This is the sling bag I have:
https://www.finnprotec.fi/webshop/tuotekuvat/585__7d133f.jpg

A conventional backpack can be slung over one shoulder, if one so desires. for small loads, i prefer either a waist pack or cargo pockets, depending on bulk.

A lightly loaded larger pack is more comfortable than an overloaded smaller pack.

Take a look at blackpowder.com possibles bags, many sizes to choose from.
Good company MTC YMMV

It doesn´t stay there unless you hold it with a hand.
I never ever want to carry anything in my hands, always want my hands free.

I have noticed that sling bags are popular among Europeans. They seem a a lot handier than a pack in tight spaces.

I worry about all the weight being on one side all the time, and permanently causing me to list to port. Is it easy to sling the same bag from the other shoulder to balance out the strain?