Carry on weight limit was not enforced when I flew this route. In fact, I've never seen it enforced on domestic flights either and I fly them monthly.
The regulation for mobile phone usage was changed earlier this year. It was previously no phone usage at all, but the authorities have now given a green light to phone usage as long as it's switched to airplane mode.
For Bluetooth headphones it a hit and miss, depends on your crew.
As for power banks, it's a strict no for using them onboard. Also do note the 20000mah capacity limit. You can probably bring them ex LAX, but you won't get past transit security with it if you have a connecting flight at PEK.