Usually sellers leave the keys with their estate agents and these are then released to you once the solicitors have confirmed the money has been paid over. It is worthwhile checking in advance exactly what keys will be there. It is a nuisance discovering that there are some doors you don’t have keys to, or that you are only getting one set of keys.
If you need instruction booklets to work the oven, the central heating or anything else, check with the sellers that they are keeping them out of the packing and leaving them on the kitchen table.
Some alarm systems need a password to be keyed in to reset them when they go off. You should get the password from the sellers, arrange for them to talk you through how the system works, and make notes.