Depending on the reasons why you missed it, your travel insurance may cover the cost of additional flights. You would have to read the appropriate section of your policy. If not covered by the policy, you would either have to cover the additional costs yourself, or forfeit the holiday.

David

providing you check the flight times on your tickets, allow sufficient travel time [depending on the flight time] baring major motorway accidents there is no excuse to miss a flight, 3hrs is called for at most airports for check in and in most circumstances 2 hrs is sufficient, less than that could cause problems getting through check in and security

wizard

It also depends on the carrier ... Ryanair/Easyjet ... forget it!