My usual advice for travel photography is long, wide and fast. The exact lens selection depends a bit on where I'm going and what I expect to shoot. For the UK (I've been there a few times) I would take (in order of utility) 18-55, 55-200 and 16 f/1.4. I find the interior of churches and old building to be fascinating, hence the 16mm/1.4. For street scenes the 18-55 is a very nice lens, backed up by the 55-200 when more distance is useful. For landscapes (and urban gardens), the 18-55 works nicely, but I would also like a macro lens for these situations. I sometimes carry the 56mm f/1.2 if I expect to shoot some portraits, it's a beautiful lens for such use.
If I were traveling to Africa or South America for wildlife photography, I wouldn't use my X-T2, but instead stick with my big Canon gear. I hope this helps, but bear in mind, some redundancy is necessary in case a lens or body fails. I've had something go wrong often enough that I always carry two bodies and multiple lenses. I'm heading off to Iceland just after the holidays and will take a combination of Canon and Fuji systems. I'm curious how well the X-T2 will work out in somewhat adverse conditions, so stay tuned for more.
Safe travels...
