Ben - COuple things I never leave without
3 Pairs of Gloves - 2 x Casting gloves, and 1 x Heavier pair for leader/wireman work if needs be... I like really lightweight casting gloves, and nice to have two pairs to rotate as mentioned above, and I like a heavier pair for playing wire man, or grabbing big scuted tails, rough jaws etc without ripping up casting gloves... a bit OTT perhaps, but a gashed finger can ruin a trip.
Footwear - This has been discussed at length, but I'm a fan of solid quality footwear... most places I fish involve wading as well as rock work, and boat work, so a good pair of quality footwear is a must.
Good sunnies are an obvious essential, but having a back up pair is a good idea, or at the very least, a floating sunnies strap to keep them on your head.
Hat - I usually take 2 or 3 hats just in case...
Buff - Small items, again I take at least 2 with me... if one gets lost or whatever, I got a back up..
Sunscreen - I'm pretty militant about the sun, so I take Factor 50 Island Tribe gel for face ( 100% block out, completely waterproof - only needs to be applied once a day ) and P20 or similar for the rest of the body.
Lightweight shirt - I much prefer the new Airwick type shirts like the Simms Solartec, or Columbia Guide II type shirts, over traditonal fishing shirts like Columbia Bonehead etc... I like the Bonehead style shirts for flyfishing and such, cause the pockets are helpful, but for jigging/popping, the pockets are usueless, and the flaps and sleeves of the shirt just get in the way when casting and jigging in my opinion...
Ski Pants - Might sand a bit crazy, but I learnt my lesson on these... nothing can put a man down like a batch of CHRONIC chafe..... especially in hot weather, and if you are wading/trekking beaches etc.... a simple cheap pair of lycra tights ( like cycle shorts without the pad ) go a loooooong way into saving you delicate bits!!! ( These are worn UNDER your shorts/pants of course!!!
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Jacket - Although most of our GT targetting locals are tropical, the weather is always unpredictable, and getting caught in a big squall can drop the temp really quickly... a lightweight high quality waterproof can save the day and keep you warm and dry when needed...
Rehydrate sachets or simialr... Most of these taste nasty, but some good ones out there... good to just have one a day for the evenings to get your salts back up, especially if you fishing super hot locales...
And last but not least, the most important, an Orion BigFoot 230 to use for chasing Garfish of course!