Kit Bags ARE noticeable, so, not advisable for trying to get a gun into a declared gun-free zone, but, notably, there are knock-offs being marketing as trendy urban/club wear, so, they are not that far out-of-place, even in urban environments, among the herbivores. I always recommend rewarding the original developers of an idea, so, have no idea about the particulars of any of the knock-offs.
First Spear is the vendor who makes HPG’s rugged nylon gear, and, First Spear has made some very interesting small packs, of various sizes and shapes, but their line-up has been trimmed, in recent years.
The Kifaru Koala is not a knock-off of the Kit Bag, but an independent development, also made to a very high standard.
The Safepacker, made and sold by The Wilderness, can be worn, with a strap, cross-body. I am carrying a service-sized revolving pistol, in a Safepacker, in that exact way, today, as I am about town, on various errands. (I have a small autoloader in a pocket, too.) One could also use one’s own straps to rig a Safepacker to be worn as a small daypack.
www.thewilderness.com
Eberlestock makes very high-quality nylon gear, too. Some of their stuff might serve your purposes, perhaps by re-purposing a binocular pouch to be a pouch for a small pistol.