I'd add OFO as an alternative to Mobike.

Since many banks work only with IE on a desktop, a mobile banking app can be useful. But it comes with all the usual hassle. (I upgraded to a new card with a chip and after two visits and hours at the bank they still can't get mobile banking to work with the new card.) Also, not sure whether Mainland banks are yet following the policy of blocking mobile apps on rooted phones.

Taobao can also be a useful app.

Pleco and Hanping if you're into Chinese.

Chinese input editor, like Google Pinyin.

12306 if you can book trains in Chinese.

Other travel apps -- ctrip, agoda, hotel chains, etc. -- depending on your preferences.

Maps.me as a backup map source.

Google Earth if you have a VPN.

Skype for calls outside China, though quality not 100 percent reliable.