A secure location is a place that FedEx can access but porch pirates (package thieves) cannot. Staffed hotel desks, FedEx ship centers, or other locations where an employee can accept a package on your behalf are great choices.
Make sure you only look for a "Fedex Ship Center" or "Fedex Authorized Ship Center" (there is a filter and key at the bottom of the map), and that they accept Ground and Express shipments.
NO "Dropbox" Locations are too small to return your package, and it's always a good idea to get a receipt or confirmation number when dropping off to confirm it's in FedEx's possession.
Your KIT may arrive 1-4 days before your first rental day so Not shipping to a secure location could result in a missed delivery or theft, leaving you without a KIT for your trip and possibly responsible for the cost of replacing the items stolen.