Alipay -Even if you use WePay, you will probably need this app too for payments and transactions as for Taobao, it's convenient to use Alipay.

DiDi -This app is for ride-sharing service (Like UBER). It's not that expensive andconvenient. English version can be found in the Play Store / App Store

Baidu Translator -Even if you can use Google Translate, this translator is the most accurate one

for Chinese translations.

Xue Fu Bao -for recharging ID card and electricity - you can use this app to check card balance,even to lock your card if it gets lost.

Taobao app - You will use this app the most for the next 4 years. You can buy every single thing using this app.

Honegood -  can be used to get codes for the water machine on each floor to get water at the cheapest rate.

Metro Man - Provides you the detailed map of metro lines and how to reach a destination (it will tell you where you need to change lines)