Also, just throwing this out there for anyone who is on prescriptions for mental health purposes (I am), please, please, please make sure you bring a copy of your prescription to the UK. Maybe even go to your US doctor to see if they know what prescription is best to switch to in the UK.
Some US antidepressants/anxiety medications are not available in the UK.
Fill your prescription in the USA and meet with a GP as soon as you can if this situation applies to you.
Additionally, make sure, if you wear glasses/contacts, to bring a copy of your prescription to the UK. It's just a good reference if your glasses break while abroad or you need new ones.
The things I never thought of.