There are several things you must provide yor pet with and several things that are optional.
Substrate
This is vital for a spider tank and several things need to be considered.
The substrate needs to provide as natural a floor covering as possible and we use a Peat and Vermiculite mix, both of these can be bought from a Garden Centre or DIY type store.We mix 2 thirds peat to a third vermiculite and this allows the tarantula to burrow if it needs to and also holds moisture to keep the humidity levels up.
Vermiculite
is heat expanded volcanic rock that is very soft and light and holds water very well. It is not to be used on its own as the spiders cannot readily burrow into it as easily as the Peat mix. It is totally inert which means it contains no harmful chemicals and is PH balanced
Peat
use moss peat from good garden stores and not plain peat as it is more like powder and dries to a dust. When this happens it is almost impossible to dampen again.
There are several other options that people consider and we will go through a few, with their pro's and con's here
Gravel- Pet shops often sell coloured gravel and people are tempted to use it to pretty up their tanks, but it is a very poor substrate that doesn't hold moisture ( except as water at the bottom of the tank) and is too hard to burrow into.
Bark chippings- Looks very nice and natural but most often is harvested from soft wood conifers which contain harmful and sticky sap. Not recommended!
Compost-Many of the prepared composts have ingredients added and some contain strong pesticides which would kill your spiders. Not Recommended! Moss Peat is generally cheaper and won't as a rule contain any other ingredient.
Garden soil/Leaves- Things that you collect yourself again are rather tempting to use but bear in mind that their is generally a whole microsystem of creatures already dwelling in your garden/woodlands and these can cause problems for your spider.
Also leaves look brilliant but hide a magnitude of things and provide too many hiding places for crickets etc. You will not be able to see any debris that must be removed from the tank (eg half eaten crickets) and so fungal infections can be harboured in the vivarium.
Different keepers use different substrates and there is no industry or hobby standard but the Peat and vermiculite mix has worked very well for us and many other keepers over the years, it holds moisture well, is dark and so shows up any debris in the tank and is generally free from any harmful chemicles or stowaway mini beasts and so this is the one we would recommend.
Somewhere to hide?
Spiders like their privacy too and you should always place in the tank something for them to hide in.They will use this hide away for when they feel vulnerable and again this is a very important piece of equipment.
All of our spiders live under plastic plant pots that we have cut in half from top to bottom,across the bottom and back up to the top again. This, when placed on the floor of your tank will make a cave and the spiders will use these quite happily.
If you would like to spend a little more money then you can use cork bark ( available from good pet stores ) which looks nicer and provides exactly the same function. As a rule of thumb the caves we use are generally a little larger than the spiders themselves and often they will dig down into their substrate to make the cave deeper. If you use a much larger pot than the spider then you can cut it at an angle so the mouth of the cave is smaller than the back.
If you have arboreal (tree dwelling) spiders a piece of cork bark or length of plastic tube/thin drainpipe cut in half and placed up against the side of the tank make an excellent vertical cave and provides the spider with a safe place in much the same way as the ground cave. Please position safely so it does not fall over! Alternatively a cave can be cut from florists foam (the green water holding one not the grey dry and powdery one) and used in the same way. If you would like to use branches make sure they are from a safe tree such as apple and have no bugs on (tiny mites hide on the joints and are very hard to see with the naked eye. Watch also for mould, as it grows very easily on old wood, if you can live without branches it is probably healthier for your spider. The arboreal species we keep have thick Nylon mesh available from Garden centres to climb on and this hardly ever needs cleaning.
We would not recommend putting rocks of any description into your tank as they can scratch a tarantula or fall on a tarantula (especially the burrowing species) or if the spider climbs and falls onto the rock its abdomen could rupture! Leaving you with a dead or worse dying spider.
( If a spider does break or rupture it's abdomen there is a way to try and save it, If you take a small piece of tissue paper and dowse it with super glue you can suture the spiders wound and hopefully it will heal on the next moult, This is a rare situation and doesn't always work but it has worked for us in the past and if all else fails??!!)
We have never felt it necessarry to place plants into a tank although a pot plant could raise humidity. Be careful when choosing plants as some may be toxic to the spider and some eg cacti could injure/pierce the spider because of spikes. Plastic plants could be used ( again be aware of the metal wire found inside the stem) even silk plants could be used although keep an eye out for mould as it seems to grow well on silk plants. None of our spiders have such luxuries and they are only needed by the keeper for aesthetic reasons, the spider certainly doesn't miss them.
Do I need to give my spider water?
YES A spider should always have fresh water to drink from and sit over to give moisture to it's underside. You can give the spider a drink in all sorts of low containers eg a jar lid or bottle lid etc.
For spiderlings a tiny bottle lid will do although the smallest spiderlings will often drink from moisture droplets on the tank side etc. For larger spiders a jar lid is sufficient and to stop the spider from drowning a piece of sponge or cotton wool can be added ( up to the top of the water level only! ) This aids the humidity levels as well!
Do not worry if you never see your spider drink they often get most of the moisture they need from their pray and if the spider is constantly drinking or sat on top of the water container you may well have to increase the humidity for the whole vivarium.