Final answer:
The best practice for traveling overseas with a mobile device is to use a secure password and avoid using public Wi-Fi without a VPN.
Step-by-step explanation:
The best practice for traveling overseas with a mobile device is to use a secure password. This helps protect your device from unauthorized access and ensures the safety of your personal information. Option 1, keeping it in airplane mode, is a good practice to conserve battery life while traveling. Option 3, disabling automatic updates, is also a good practice to prevent unexpected data usage. Option 2, using public Wi-Fi without a VPN, is not the best practice as it can expose your device and data to potential security risks.