What can be difficult is understanding just how much data you use when you do basic things on your phone - like a couple of searches on Safari.
So, I figured I would try out using my mobile data briefly to see how much I used.
I turned on my mobile data and data roaming, having earlier made sure that all apps were turned off for mobile data use.
I reset my usage settings to zero, then I turned on just Safari, and did a couple of quick searches about the monument we were visiting, looking at just one result.
I then looked at my data usage for that couple of minutes - to discover that I had already used 11MB, at a cost of nearly $5. And I hadn't even found an answer to the question that I was looking to answer!
So my lesson for the rest of the trip? Save my mobile data for an emergency!