Thanks everyone, that's a wealth of great information, really really helpful as I get to actually packing and not planning.
It's a great point about taking less shots pre-digital. One roll for the holiday, those were the days!
I took one roll on my (2 weeks in Portugal) honeymoon, seems crazy now but holidays meant disposable 110 cameras and feeling i'd gone the extra mile by getting 'matte finish' prints from the chemist for me then.
Conversely, it's also helpful about breaking it down to hours per day available.
I'm taking two cameras for two films - fast/slow or c41/b&w - rather than for two lenses. A typical day is one camera, two lenses (these are RF lenses, so tiny to carry)
I really want to take B&W so I can take shots 'for me' and print some of them when I get home but I have to take C41 since there's an expectation from everyone else that family memories will be in colour.
But it's an excellent point about too much variety - I might just limit it too 400 speed, Portra and HP5 (perhaps just a couple of rolls of Ektar as a treat.)
I agree that choice can be a burden but I've not reached that one camera, one lens, one roll, one shot (!!bring the 8x10!!) state of nirvana just yet!
I already have the film so would rather bring it if possible. (I'd totally forgotten about Boots in the UK.)
I can't control radiation so will just go with it, dodging X-rays wherever possible.
Llangollen - railway -> summit, consider it done! Come rain or sleet, mizzle, mist etc, it's a definite!
I'll try out 40-50 rolls tonight for a practice pack, see how it looks. I am trying to treat 35mm film with a little disdain for this holiday I guess, something to be burnt through in the hope it encourages me to capture more of me and my family and where/who we were at this moment in time. (No digital for this trip.)
In normal use with 35mm I never look at a contact sheet of mine and feel I got too many of the same thing, I'm not one for multiple takes or bracketing etc.
Thanks again all! Feel free to keep any thoughts coming, not only for me but for anyone else reading this at a later date or also planning that big trip.