Don't really know why you need a sim just to go on holiday. Just use Skype on your phone or what's app, line etc, getting wifi is not a problem in most places.
I could probably get by OK, but having internet access on the go is great for finding your way around or googling the things you're seeing on the spot' as it were.
I bought a local sim with unlimited data in the US the last time I was there and it helped me to get so much more out of the trip.
Not essential, but would be nice.
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