The nether is a very hostile and repetitive enviroment. I hate it feom the time my arrow missed a ghast and hit a random pigman behind it.
Some time later, I tried repeatedly to survive in the nether without contact wih the overworld, but without success. First I tried to take just some iron sword, a pickaxe and some starting food. I thought I'd get food and material (while in one of my mini-bases) from the pigmen (rotten flesh, gold) and from nether fortresses. This failed after my pick broke. Every other try, I took more and more items, but without success.
So here comes my question: What items (minimaly) shoud I take to the nether to be able to survive for any period of time? Which items are crucial to survive?
I woud also say that being able to survive means to be possible to survive whatever mother nether gives you, and surviving means "staying alive".
Best Answer
Let's identify what is needed to "sustain a living" in minecraft, provided this living is more then standing still in a hole. Basically the things you want to carry around with you all the time in a survival world or that you want to accumulate quickly in a base you set up in a new world.
First of all: Food. Keeps you be able to run, jump and fight, regenerates health qickly (as of 1.9+) and is needed to survive longer then until you starve to death. to get this take two stacks of eggs with you as well as some redstone materials and build up a fully-automatic chicken farm that will provide you with cooked chicken (and feathers).
Then: All the tools and armour. You need a sword, pickaxe and shovel in the nether (axe not really necessary) and the four armor pieces would be nice to have. A bow is quite important as well.
To properly use your tools and armour you could take an enchanting table with you and enchant them after you made a new tool. Lapis Lazuli would run out sooner or later though. If you bring a cleric villager for trading gold and rotten flesh for emeralds with you anyways, you could trade lapis lazuli from him.
As for a bow, the only way other then to bring an ample supply of string with you would be a fletcher villager that trades emeralds for a bow and for arrows. Otherwise you'd get feathers for arrows only from chickens - a stack or two of eggs would suffice to get a chicken farm going. Flint you can get from the gravel patches in the nether.
Then there is smelting. Bring a stack of furnaces with you so you never run out of them if you loose some (no stone available!) and bring a bucket with you. You can use a lava bucket as fuel or coal from wither skeletons or blaze rods. You need to smelt stuff, as the only solid (ghast-blast proof) material you can get easily in the nether is nether brick and this is a lot easier to get by smelting nether rack. Also, you may have to cook your food.
That's pretty much what I can think of at first. To re-iterate what you should bring with you in case you make your stuff yourself in the nether and don't have mending-enchanted gear to bring with you and also if you don't bring villagers or animals with you:
There is only one very important thing left: Bring a bed with you and once you are in the nether take a short nap! (just kidding)
footnote: In fact, there are: In nether fortress chests. I would deem this as a too scarce source of diamonds to repair your tools, though. And hoping for zombies to spawn as a zombie siege when killing zombie pigmen and hoping for them to drop an iron ingot will also yield far too little resources.