In all climes/terrains, my Ranger takes along extra clothes. These are always camouflaged to the appropriate terrain type. In woodlands, woodland camo. In the arctic, snow camo. "Stoneflage", or clothes in various shades of grey, for any terrain.
In the arctic, Cold Weather Outfits, and a white fur cloak are a must. Rings of Warmth or armor with Energy Resistance (Cold) are handy. I don't have
Frostburn, but MerricB says no skill is required for snow-shoeing/skiing (although Balance would be good). Boots of the North and/or Waterwalking would also be nice (some GMs will allow Boots of Waterwalking to work on snow & ice, others won't!). Long white scarves for wrapping the face & head, gloves, and over-mittens are also useful. The cloak should have an integral hood, and all outer layers should be wind- and water-proof. At least water isn't hard to find, here. Melt a mess of snow or ice in a one gallon pot, and you've got all you need! Crossing ice can be safely accomplished via ropes and/or poles, or anyone with a DC:15 Survival check.
In the desert, khaki/tan is the basic camouflage color. Clothes and cloaks should be light-colored, light cotton, and absorbent (to ward off incident solar radiation, and trap and keep sweat as long as possible, so the evaporation will cool the adventurers). Long head-and-neck scarves (shemaghs) are useful for keeping the dust and flying sands out of noses, mouths, and eyes. The Decanter of Endless Waters is, indeed, worth
more than its weight in gold, in such cases. Rings of Fire Resistance or armor with Energy Resistance (Fire) will also work for keeping the heat off. Don't forget, though, that the desert is cold at night (as water - which the desert lacks - moderates temperature). So the bedroll & winter blanket is often a good idea, too. If travelling by wagon, fuel will need to be brought, as plant life is rare, in the desert. Fires may have to be made with "fuel pellets" (dung), even if it comes from the PCs. Lacking a Decanter of Endless Water, also bring along a water-barrel. Waterskins are a must. Hard-sided canteens are even better, if available. Finding food is also at, at least, a -2 Circumstance Penalty. Water found in the desert is often poisoned by minerals. DC:15 Survival check to recognize this fact. Effects vary (Gypsum, for instance, can cause temporary blindness).
Swamps are best handled via magic (although 10+ ranks of Swim can also work, if you're high enough level to have them). Boots of Water Walking are nice, but it is rare for the whole party (plus mounts, familiars, and animal companions) to all have them! Another
possible solution is Mizu-gumo, or water-feet. These are like waterskins, but with snow-shoe-like straps on the top. Wearing a pair on your feet allows you to make a Balance check to cross water (DC:10 for calm water, DC:15 in chop). Adding a staff with a waterskin on each end allows a "third point of contact", when needed.
This method of getting around is nearly invalidated by the lack of Balance skill accessability, however... If you have a Bard/Rogue capable of using it, a collection of "gas-bags" filled with lighter-than-air helium, hydrogen, or marsh-gas will add to bouyancy, but may be flammable... You may be better off ignoring them.
Horses' hooves will swell and crack, after enough time in the water. Keeping them dry can become important. Some mink-oiled leather "booties" can help solve that problem. Boats and/or barges (kayaks are best, if they exist in your world) may also get you through, where the marsh channels are wide enough. More usually, a DC:15 Survival check will allow a skilled Barbarian, Cleric of the Travel Domain, Druid, or Ranger to pick a safe path through the quicksand and stay on the firm(er) ground. Rope is good, too, as are items allowing water-breathing. Also, good water may be hard to find, and getting a fire lit in the muck will incur
at least a -2 Circumstance Penalty, as all of the fuel is very wet. A tinderbox (not just the flint & steel listed in the PHB) is a life-saver, here. Water is easily available, but the pot to boil it is more necessary. Metal items tend to rust, so weather-proofing them (if available) is a necessity, and oiling them, if not.
Insects and diseases are common, in marshes and swamps. Magic is the best way to deal with this, but herbal medicine and such-like may suffice. Many insects can be chased off with smoke, citronella, pine sap, or other such cures. Most diseases can be cured with herbs (such as quinine vs. malaria).
Cure Disease and
Repel Insects are still the best bets, though. A wand of each would be nice!
Swamps and marshes are also very hard to get through. The muck, water, and thick underbrush make travel difficult. The acquatic animal life, insects, diseases, etc., don't help. The frequent mists and fogs make navigation tough. The constant wet conditions make iron or steel rust, and leather rot. Waterproofing all leather is a must. As mentioned below, hammocks to allow sleeping above the muck are also nice!
Jungles have many things in common with swamps, except they tend to be even less open, if possible. Paths have to be found, or hacked. Machettes are pretty much a necessity. The conditions are more usually hot AND humid, so you want to expose as much skin as possible (hence, little armor). Heat Exhaustion/Stroke are even more common than in the desert. Insects and diseases are also very common, here.
The Druidic (and, as of 3.5e, Rangeric) ability of
Woodland Stride can come in very handy, here, allowing those PCs, at least, to slip through any non-magical obstructions made of plants. Magic items confering this, or the
Pass Plants capability, are all very nice, in the woodlands and jungles.
For acquatic terrain, 10+ ranks of Swim seems a no-brainer. More, if you wear Medium or Heavy Armor! Climb & Jump, for getting from ship to ship. Profession (Boater, Sailor) for getting around by Boat/Ship. Some Rope Use, if you plan to throw grapnels, a lot. Again, items of Waterwalking and Water Breathing are probably going to be necessities, sooner or later. Rogues, or others with Balance skill, again might like the mizu-gumo. Items which control the weather are also quite nice. The Decanter of Endless Water is still quite useful, as sea water isn't drinkable, and the gallon pot (and a waterproof tarp) can be used to collect drinkable steam from boiled sea water. Knowledge (Geography) is needed for navigation (and available to Bards, Rangers, Sorcerers, and Wizards). Survival is still useful for gathering drinkable water, and fishing (or otherwise finding food). A great many spells probably work differently, if at all, underwater!
In mountain-climbing campaigns, Climb skill is a no-brainer (although not everyone has access to it as a class skill), and Rope Use limits how far you can throw a grapnel. All PCs should have a Climber's Kit worked in as part of their armor. Everyone should have rope, and more than 60'. Ropes of Climbing are always appreciated by climbers... Those without climbing skills should have a pair of Boots of Spider Climbing, wherein the spell is ALWAYS ACTIVE. This will allow them to run up and down the rocks without problem. The Cloak of Arachnidia also works well, for this. Note that, when croodling along the edge of a cliff, crossing skree, etc., that Balance may well be needed, but is generally unavailable to most PCs... This can be a problem! Jump may also come in handy, and is a bit more available. Items of
Levitation and/or
Faether Fall are also neccesary, for when your luck runs out. Adventures in the high mountains may need time to acclimate to the high altitudes, as well as arctic adventuring gear.
One of these days, when I get a decent place to work (and get around to it!), I need to write "The Ranger's Handbook", and include all of that kinda stuff, as well as all of the extra bits of little gear (like those hammocks, compasses, candle lanterns, ascenders, waterfeet, ice-climbing foot-spikes, snow-shoes, skis, etc.) that you can read about in any good survival manual... (Can you tell I've read just a few? 
Hey, EVERYBODY needs a hobby! 
