Galvanized trailers cost slightly more, but require less maintenance, especially if they will be dunked in salt water. Galvanized trailers offer the most durability in the salt water environment. Trailer tires are often much harder to purchase from tire stores, and it is often much harder to get service for a stranded trailer. Carrying a spare tire will almost always save you trouble if you get a flat. They're relatively inexpensive, and should be considered, even if not required, especially if you're towing after dark.
Lights commonly required include sidelights, taillights, stop lights and turn signals.
Safety Chains - Safety trains connect the tongue of the trailer to the towing hitch. If your coupler fails, the chains will prevent the trailer from falling forward and potentially cartwheeling over your car. The chains should be crossed under the hitch to form a cradle. If they are not required in your state, consider getting them anyway. Most states require a license for a trailer, and may have equipment requirements for lights and mirrors.