Insurance policies contain reasonable care conditions that require you to take care of your insured property.
Travel insurance policies often exclude claims for belongings that have been left unattended in a public place. Each policy will contain its own wording and details of what situations are excluded. Check your policy for details before you travel.
Generally, if you leave your belongings unattended in a place like a train station, park, restaurant or beach, any theft or loss will be excluded by the policy.