An EHIC entitles citizens of the European Economic Area (EEA) and Switzerland to free or reduced-cost healthcare in any of the participating countries. It covers you for any medical treatment you might need, whether you fall ill or sustain an injury during an accident, whilst in that country, it does not cover for repatriation if you have a serious accident or illness.
In addition, it does not cover you for lost luggage, stolen items or cancellation, all of which can be provided by a travel insurance policy.