The single best thing you can do for your data usage before any trip is download offline maps. It takes five minutes at home, works completely without a connection, and removes the anxiety of not having signal in an unfamiliar place.
How to download offline maps
Open Google Maps. Search for the city or region you're visiting. Tap the area name in the bottom panel to open the location details, then scroll down and tap "Download." For country-level downloads, search the country name instead.
The download covers turn-by-turn navigation, search for businesses and addresses, and basic transit info. It doesn't cover live traffic or real-time transit schedules (those need a connection), but for getting from A to B in a city, offline maps are fully functional.
Downloads are stored for 30 days by default, then auto-delete unless you update them. You can change this in Maps → Profile → Offline Maps → settings.
How much storage do maps take?
A city like London or Paris is about 100-200MB. A whole country download - say, Japan or the whole of France - is 1-3GB typically. A phone with 128GB storage can hold all the maps you'd ever practically need for a trip.
Download on Wi-Fi, not mobile data. Downloading a full country on a 4G connection will eat your data allowance before your trip even starts.
How offline navigation actually works
Once you've downloaded an area, you can search for addresses and navigate to them with zero data. The map tiles load from local storage. Turn-by-turn voice directions work. You can zoom, pan, and explore the map exactly as normal.
What doesn't work offline: real-time transit schedules, Street View, live traffic overlays, photo contributions, and reviews. These all need a connection.
Offline Maps in practice
I always download offline maps for every city I'm visiting plus a buffer region around it. If I'm staying in central Kyoto, I download all of Kyoto plus the surrounding Kansai region - so day trips to Nara, Osaka, or Arashiyama are covered too without any extra data use.
For road trips, download the full route region. Driving from Barcelona to Valencia? Download eastern Spain. The offline tiles load smoothly during navigation even at highway speed.
Alternatives to Google Maps offline
Maps.me is fully offline by default and uses OpenStreetMap data, which can be more detailed in rural and developing-world areas. It's free. Worth having as a backup, especially in countries where Google Maps data isn't as comprehensive.
Apple Maps also has offline download capability now (iOS 17+), though coverage is patchier than Google for non-English-speaking countries.
The data saving upshot
With offline maps downloaded, navigation uses zero mobile data. That 5GB eSIM plan you bought goes entirely toward the things that actually need a live connection - WhatsApp, checking restaurant reviews, Instagram. It's a genuinely meaningful saving over a two-week trip.