There are two things you need to consider when you think about travel insurance. Firstly medical and emergency insurance. Secondly the insurance of everything else; your belongings, paperwork and flights.
The medical one is the biggie, because of the cost of medical bills and things like medical repatriation a medical bill can literally cost millions. So it's pretty important to get it right.
It's worth getting your insurance before you by your flights, that way if you have to cancel for some valid reason, you should be able to claim back the flight costs.