All my suggestions are around moving! Selling, storing or binning your things. Turning off utilities. Selling house or car.
I would never suggest giving up bank accounts, credit cards, drivers license, voters registration, etc. If you moved to another state, you might switch those things, but if you move to the UK, my advice would be to leave as is.
Truly, other than packing/moving, I wouldn't suggest much regarding the US aspect.
ETA: I did get a haircut right before I moved, in case I couldn't find one right away. I did stock up on certain things that I knew would be hard to come back in the UK -- certain clothes and makeup mainly.