Why the timing matters
A few of the apps you will rely on in Chengdu ask for an SMS verification code, an existing account in good standing, or a card that needs to be added and confirmed. All of that is simpler when you are on a network and phone number you already trust, rather than trying to receive a verification text on a new SIM in an unfamiliar app. Android phones are a particular risk: if your phone relies on Google Play for installing apps and you have not put anything else on it in advance, you may land with no straightforward way to add new software at all, since some foreign app stores and downloads are not reachable from inside mainland China. iPhone users are less exposed to this because the Apple App Store keeps working, but the account verification issue still applies to both platforms.
Treat the setup as one sitting rather than something to fit in between other packing tasks, since each app tends to reveal one more step once you start.
Payment apps first
Alipay and WeChat Pay are the two mobile payment systems that most shops, restaurants and transport systems in Chengdu expect, and QR-code payment has largely replaced cash and card terminals in day-to-day transactions. Both apps let a foreign visitor link an international bank card, mainly Visa, Mastercard and Diners Club, without opening a Chinese bank account, which is the detail that makes them workable for a short trip. Set up both if you have the time, since one occasionally rejects a card or a transaction type that the other accepts, and keep a modest amount of yuan in cash as a fallback for the rare vendor who takes neither. There is no tipping culture in mainland China, so you will not need to budget for that on top of whatever the apps handle.
Maps that work there
Google Maps is not usable in mainland China, both because Google services are blocked and because its location data for Chinese addresses is unreliable, so plan around it rather than counting on it as a backup. Amap (高德地图) and Baidu Maps (百度地图) are the apps most people in China actually use, and while both are mainly in Chinese, their search and navigation functions are workable once you know roughly what you are looking for. Apple Maps runs on local map data inside China and is a reasonable option if you prefer an English interface, though it tends to be thinner on local detail than the two Chinese apps. Whichever you choose, open it before you fly and get comfortable with searching in pinyin or pasted Chinese characters.
Getting a ride
Didi is the ride-hailing platform used across Chinese cities, including Chengdu, and it has an English-language mode built into the app that makes ordering and tracking a ride manageable without reading Chinese. You can also reach ride-hailing through Alipay or WeChat if you would rather not manage a fourth app, since both have Didi's service built in as a mini-program. Registering an account and adding a payment method before you travel means your first ride from the airport is a matter of typing an address rather than troubleshooting a sign-up screen at midnight.
Translation that works offline
A camera translation app that can read Chinese-only menus, signs and transit information is one of the more practical tools for a first trip, and the offline language pack is the part people forget to download in advance. Once the pack is on your phone, translation works even without a signal, which matters on a metro platform or inside a restaurant with poor reception. Test it at home on a printed Chinese label or a photo pulled from the internet so you know how to frame the camera and how long it takes to render a result.
Landing in Chengdu with it all ready
With payment, maps, a ride-hailing account and translation already set up, your first hour at either of Chengdu's airports looks fairly ordinary: you find a SIM or connect to airport wifi, open Didi or the ride-hailing mini-program inside Alipay, and enter your hotel address either by typing pinyin or pasting the Chinese text you saved earlier. From there, paying for the ride, checking in at the hotel and finding your first meal all draw on the same handful of apps you already tested at home. If something does not work as expected, the fallback is the same one that always works in China: cash, a paper address, and asking someone to point.