When I first went urban sketching I brought way too many things with me the first few sketch outings. I wasn't sure what was 'normal' for an urban sketcher to have along out there in the wilds of the urban setting.
I also worried because I wasn't sure what supplies I might want or need to actually use, so I brought several grades of hardness in lead pencils, sharpeners, mechanical pencils, extra leads, several kinds of erasers, masking tape, bungy cords (not sure what for), pens of all sorts, watercolors-and palette-and water jug (a too large water jug), colored pencils, and, several kinds of small and large sketchbooks.
I prepared myself for changes in weather, both in the layers I was wearing...and in the supplemental garments to be found in my sturdy rolling cart. I was ready for wounds, hunger, mapping my journey, taking out trash, having a place to sit, a way to clean hands, preventing sun burns and mosquito bites...and....the list was longer, but I'm too embarrassed to go on listing items.
My first urban sketcher lesson learned: One's gear will be heavy if one's packing philosophy includes the phrase 'just in case.'
So, now I try to be a minimalist. I decide what supplies I would enjoy using this particular day...and that is what I will happily use no matter where I wind up or what I find to sketch. I try to limit myself to what will fit in my pockets, though admittedly, I have some jackets and vests with good-sized pockets. Second-hand shops are great for garments like that.
This is one of my smaller sketch kits: black and white ink pens, a mechanical pencil, an eraser. One pen is missing, because I used it to make this sketch.