Medical coverage and pre-existing conditions
Ensure that medical cover is adequate for possible expenses in the country you are going to visit. In some parts of the world medical costs can be very expensive. Remember that whilst you may have an GHIC/EHIC card which provides reciprocal emergency health care, this only applies to emergency treatmnet and will not cover additional fees such as repatriation costs back to the United Kingdom etc.
In order to ensure you are covered correctly it is very important that you declare any pre-existing medical conditions you or anyone you are travelling with or intend to stay with may have.