1. You need a minimum of 10 to 14 days to offset the possibility of problematic weather. A tropical storm, wind in the wrong direction, red tides, cold front, are just a few of the problems you may encounter. I don't care if someone, agrees to call you just prior to departure. Conditions change with little of no warning. That light rainstorm of 1 to 2-inches can turn into 12-inches pouring muddy water into the backwater canals you were going to be fishing.
2. Take a fly tying kit if you are a feather bender. The stuff you may have tied up prior to your adventure may be wrong or not suitable to the conditions encountered. If you don't tie go with someone who does or find someone who can produce what you need. If this is not possible, get an experienced fly shop employee to recommend a broad cross section of general purpose flies to take along to supplement the flies you should buy at the local fly shop.
3. Have the electronics (phone, iPad, or ?) that allow you to connect to the internet for tide, wind and weather information. Learn how to use the software before you go. Understand that predatory fish respond to moving water to feed. Being in the right place at the right time is what it is all about.
4. You need more than one line. At a minimum I would have a floater, intermediate sinking line (full or 26+ foot sink tip), and a fast sinking line (300 grain is about right). Each should already be mounted on a reel spool to change-out at will.
5. You need more than one rod of the principal size range you plan on fishing. If that's an 8-weight you need two eight-weights, or one eight and a seven, or one eight and a nine.
6. Buy large spools of fluorocarbon material so that you can construct or repair any leader and have various sizes of bite tippet material at hand (I lost a 40-inch Snook on 25-pound test because I didn't have some 30-pound test with me). Learn how to tie the right knots. I'm not talking about the knots used for trout fishing. If you need help with this go into a shop for assistance or just look on the internet for instructions.
7. Make sure you have a reel that can standup to saltwater conditions and is capable of handling the fish you've targeted. I've watched a many "good" fresh water reels that are "saltwater friendly" blow-up. You may get an unplanned opportunity to score on a truly large fish.
8. Use a waterproof pack for your gear. Nothing is more irritating than filling your fly boxes with saltwater. Fanny packs are only great in shallow water anything more and they suck.
9. Get a stripping basket unless you have more than two hands to control your line. If you get one of the collapsible types make sure it works to your satisfaction before taking it along.
10. Carry a idiot proof point & shoot waterproof camera that can be easily accessed. If your holding the fish, someone else has to take the picture.