Here's a list of things you must do before leaving Cambodia:
1. Set up BOTH wechat and alipay with your local credit card. Learn how to use their features by watching some videos. You can do everything on wechat, most on alipay.
2. Get a Chinese SIM either in your country or on arrival at the airport.
3. Install Astrill vpn on your laptop, pad, and phone. Pay for a three-month subscription. Make sure it works before you leave. It's not great, but it is simple and has proven to be reliable for the past decade. Right now the only servers that works on the phone or pad are UDP servers that you have to test once you get to China. They change almost daily, depending on how bored MSS is.
4. Install the following apps: Didi(滴滴), 12306(中国铁路), Rednote(小红书), Ctrips(携程):Didi for getting rides everywhere, including airports and railway stations, you can link up with your verified wechat/alipay account. I think now most apps allows link up with wechat/alipay, if not all. 12306 for train tickets. Rednote for searching for any strategy for anything you want to do. Ctrips for booking hotels and domestic plane tickets.
5. Wechat's mini apps are extremely useful. Learn it before leaving for China. Most public institutions like the Forbidden City or Palace Museum has their only mini app in wechat that allows you to quickly make a reservation.
6. 美团买菜/饿了吗 are the two delivery apps that will make your life so much better, like getting food, fruits, medicines, toilet plungers, and anything you want delivered to you within an hour.