Phone, wallet, external battery are my must have basics. Everything else is optional.
Seriously, when it comes to bags, I prefer a specific size. Like the medium PSII, medium box bag or boy bag. I like small but not too small crossbody bags. I HATE totes. Because they fit so much, I will find ways to put all kinds of stuff into it, so I always end up with a very heavy bag. So the Pom Pom bag by @floralpunk is an amazing compromise ! It has the perfect size for me to carry around all of my everyday stuff without being too big. Everyday stuff are a camera, my phone, notebook, keys, make up stuffs and sometimes a bottle of water. It looks smaller than it actually is, because it fits so much. And I don't just recommend this bag for everyday use because we sell it, but because I actually think it's a great bag haha. The only thing I don't like it, because it's simili, when it touches your skin and you sweat, it becomes really sticky. But I don't wear shoulder-free very often so it's fine : )