out of the bush right now i just carry what is in my pockets. on the way to and from school i have my bag of books and things, but that is somewhat specialized.
i hae been from one extreme to the other. at one point i carried nothing at all, most days even forgetting to put a knife in my pocket (pre-knife knut days). then somehow i ended up toting a fully loaded backpack everywhere with me stocked with all kinds of gear. looking back, it was a sort of ill prepared BOB. things like food, water, raingear, extra clothing, etc.
now i only gauranteed to be carrying my two EDC knives, my keys, my back pocket paper cake, handkerchief, sharpening stone, matches/lighter, lip balm.
if i have a jacket on, i normally have something like gloves and a balaclava in the pockets, and sometimes i toss extra stuff in there too.
i have been casually looking around though for a low-key small backpack for carrying some basic stuff like water and a snack and maybe some raingear if the weather looks bad. i like a backpack though because if i need to i can load it up heavy and still carry it comfortably and securely.
i do like shoulder sling bags like that one though, and am still searching for the perfect combination of pockets and materials. i am getting closer and closer to biting the bullet and just making the perfect one.
that bag looks good, i like the gear assortment you have in there. personally, i live in a suburb, so i don't spend alot of time away from a stash of resources except when hiking, and then i have my whole bag on me. when i do take day trips to the city though i normally have a shoulder bag with the things i mentioned above.