I used to lug around a heavy tactical bag filled with every thing needed to run away from home in a instant. That got really old. These days I don't carry a bag with me unless I am going to be spending a minimum of several hours in a fixed place otherwise my "EDC" bag stays in the truck if I bother to bring it at all. Okay, so here's what's in it: some ball point pens and mechanical pencils, A notebook and manuals applicable to the task at hand. A hand full of cough drops, a small bottle of ibuprofen, a bandana, some ear plugs, a hard sided eye glass case, a couple tea bags, some stevia packets, 15' paracord and a carabiner or two (I practice knots), a small bottle of hand sanitizer, a water bottle, a handful of napkins and paper towels in a plastic bag, a SAK Compact and a LED mini-Maglite.
The truth is when I carry it, my bag is more for what I might find along the way rather than what I all ready have. There are always the other things that might be added, a hat, balaclava or keffiyeh, gloves, lunch or snacks, a paperback book. If I'm at a farmers market or swap meet I'll include a cloth shopping bag.