While we always pray for the best, some bad situations can arise where it is necessary to have travel insurance.
Typically, if you pay for your flight ticket by credit card (I have received this with MasterCard and Diners Card) you will get basic insurance cover for free, which you could top-up. However, even the top-up option may not be as flexible as you need it (e.g. if you plan to extend your trip or are covering multiple countries at your own pace as a backpacker), or cover those adventure sports that you indent to participate in.
You need to read those Terms and Conditions for whichever product you are considering to make sure that it meets your particular needs.
When deciding on a travel insurance product also consider WorldNomads.com offering, where you can buy, extend and claim online even after you’ve left home. It is available to people from over 140 countries and designed for adventurous travellers with cover for overseas medical, evacuation, baggage and a range of adventure sports and activities.