I am terribly sorry to learn of your loss, please accept my condolences.
Florida law is designed to ensure that the wrong party does not come and take possession of the deceased person's assets (keep in mind, the law is written to cover many situations, not just yours, and there are unfortunately many cases where there is a dispute over who is entitled to the belongings or assets of the estate).
This leads to a somewhat complicated set of rules that blocks the landlord from releasing the property without a court order (issued in probate), or the passage of 60 days (at which time the landlord would take possession of the belongings).
Given the fact that you have long distance travel involved here, I would suggest that you retain a FL attorney for the purpose of filing a probate case for your son (you can do this yourself if you feel confident in completing the paperwork, and then have a process server file the documents with the court - but the cost of having an attorney do this for you is probably worth it simply to ensure it is done properly and to avoid the hassle and to ensure there is no error).
This article here explains the issue in a little more detail, and gives you references to the applicable FL Statutes: http://lieserskaff.com/how-florida-landlords-should-handle-a-deceased-tenants-personal-property/
You can find Florida attorneys local to where your son was living using the State and local Bar Association directories, or private directories such as www.AVVO.com; www.FindLaw.com; or www.Martindale.com (I personally find www.AVVO.com to be the most user friendly).