If you’re often connecting your Mac laptop on the road through a mobile connection (phone, USB dongle, etc), TripMode will show you which app is using how much bandwidth and will allow you to disable internet access for it.
This can both save you money as well increase the connecting speed of the apps you’re actually needing. It also helps identify apps that connect on the net even when you wouldn’t expect them to.
TripMode costs $7.99 but there is also a 7-day trial which turns into a 15-minute/day free version after that (works fine if you’re on relatively short train commute). Get it here http://bit.ly/1M1mCbY.