Make sure to turn off automatic updates on your phone, tablet, or laptop before connecting to in-flight Wi-Fi; especially, when the Wi-Fi plan comes with a limited amount of data size restriction.
You can purchase an in-flight Wi-Fi plan on many international routes nowadays. Some may give you unlimited data for a limited amount of time. Some may offer you with cheaper solutions based on the data size limitation. When it comes to the data size, it’s not just your email or Facebook Messenger. The background processes consume a lot of data behind the scenes especially during the updates. Be sure to turn off the automatic update, GPS, and any unnecessary background process that may consume a large amount of the data.