MacBook eating mobile data allowance.. how to control?

Hey, I just landed in Australia with my MacBook Pro.

Compared to the UK, their broadband internet sucks - but the 3G/4G is much better and has more generous data allowances.

I'm used to 76MB, unlimited home internet in the UK and only use a few GB of mobile data a month, as I was mainly at home or in the office; however here, I'm outside a lot of the time, often on my MacBook.

15GB data on a SIM for my MiFi unit seemed very generous initially, but vanished in only a few hours!

My feeling is that Apple haven't really considered that some people use Macs on limited data allowances; because there is no obvious button for monitoring or controlling data transfer.

I could easily have eaten that 15GB through Dropbox, OSX downloading updates, or OSX Photos deciding to back-up/download photos - all kinds of processes that would decimate 15GB without trying.

Again, I just don't feel Apple have considered this, as I can't see any feature for controlling the situation. I'm sure I can turn off certain features like automatic updates; but a single button for 'I'M ON MOBILE INTERNET, DON'T WASTE DATA DOING STUFF I HAVEN'T DAMN ASKED YOU TO DO' would be ideal.

Any recommendations for monitoring and controlling how much data is being eaten?

I'm running the latest version of OSX Sierra.

Cheers