There's no obligation for you to take out any insurance. If you choose not to take out the airline's insurance you might find it hard to get specific 'flight' insurance since most of the policies on offer are for general 'holiday' or 'travel' insurance, which includes many things that 'flight' insurance doesn't.
If you're taking out holiday insurance anyway, there's probably no point in taking out flight insurance since this will only duplicate some of the cover you've already got.
Similarly, if it wouldn't really matter that much to you if you had to cancel your trip (and you're not taking any valuable items in your luggage) you might feel happy to dispense with any form of flight insurance. (I take occasional day trips to Spain, Italy, etc. I don't bother with flight insurance because it wouldn't be a great loss if I had to cancel my trip and I don't take any hold luggage so there's no point in paying to insure for loss of luggage).
If the '1976' in your username is your year of birth (i.e. you're under 40), you can get travel cover for a whole year, for as many trips as you like to Europe, for �22.50:
http://www.moneysavingexpert.com/insurance/che ap-travel-insurance
Chris