I had a taxi arranged by my agency to pick me up and within the hour in London I already stepped into HSBC (who wouldn't do a darned thing until I had proof of address) and bought a mobile phone. I think I had a few £s from a recent trip and I probably topped up when I was cruising the high street. Then I met my new work colleagues and started calling letting agencies. Jet lag wasn't going to get the best of me!!

People's must dos will vary with what reason they came to the UK. I was on my own with no help so my priority was finding a flat... see, getting a mobile number was so agencies could call me!
TC are sadly going out of style, but they saved me my first time abroad when I left my bank card at home.

I was once stuck in rural Rwanda without cash and the only ATM and banks were in the capital. I always remember that lesson and remind myself that cash is always a good thing to have because you never know what will happen!!
I usually carry a hard currency that will be easy to exchange in a foreign country if I can't get to an ATM easily enough. In Africa, I had USD in one pocket, local currency in another and TC stashed somewhere else... plus a debit card and credit cards!!