The famous London weather is very unpredictable and if you are not from London and planning to visit, here are some tips on what to take with you at all times.
Unfortunately you have to carry it with you all the times, you never know when you might need it.
It sounds contradictory but you have to have them at all times as well, sun can come at out the most unexpected moment.
It can get hot or cold in a matter of seconds so scarf will protect you from that in style.
Running around in high heels and sight-seeing or shopping might be fun for a while but at some point your feet will need a rest so you should have a small pair of flats in your bag at all times.
Large glamorous bag
To carry all those things above you will need a large tote bag that's big enough to fit it all in and glamorous enough so you don't stand out from the London crowd. Your bag is your fashion statement. I would normally recommend a Michael Kors bag but here is a tip, everyone is wearing a Michael Kors bag (looks like MK has planned world domination) therefore if you want to be different any other bag would be great. I am guilty of indulging into MK bags as well so you see what I mean.
Travel card that will take you on buses and underground, you can't live without it.
Or any other phone with interactive map. You will be lost. Many, many times.