Insurance: When budgeting for your trip. Make insurance part of the have-to list. Purchase your insurance the moment you book your trip, that way unforeseen circumstances occurring before or during your trip may be eligible for coverage. Many insurers will not insure your trip within a certain window after your deposit is made.
Does the location you're about to visit require preventive inoculations? If so, it's advisable to check in with your local hospital's travel clinic to have that taken care of.
In locations where a passport is needed, it's advisable to make a copy of it to leave with a trusted friend, along with a copy of your credit card in case of loss. Whomever has the copy will be able to make arrangements for a replacement. It's not a bad idea to have a backup credit card as well. Just to be safe. Never keep them both in the same location, ie, your wallet.
Your travel advisor can also act as a backup contact person. Someone you trust who can take care of issues that may arise.
Make sure you know whether or not you need a VISA for the country you're visiting. See the article on ETIAS.