We ordered SIM cards from Giffgaff a few months before travel, so inexpensive and worked perfectly, also can keep SIM and add time and usage on next trip to Italy. Also terrific free app for London and everywhere we went was Citymapper, it gave directions for walking, any transport and finding things nearby, a super “get me home” feature, it was invaluable. Along with your UK plug adapter take extra USB ports for all your charging, most hotels only have UK plugs. Take your smartphone, you will use it everywhere. Cash is almost none existent in UK, it’s tap everywhere, so make sure you have a chip credit card, or better still put it in your phones virtual wallet, you can even tap going in (make sure to tap on exit) of tube stations. Many sites have QR codes that download a guide for site. Also makes buying tickets rail, excetera so much easier and cheaper than at station. Phones have become the new “guide, travellers check, map” of travel, don’t leave home without it!
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