What do I need for my gerbil?
The tank
You'll need at least ten gallons for each gerbil. You will never need a ten-gallon tank for gerbils, and you should never own a ten-gallon tank for gerbils. The reason for this, is that no gerbil should ever live alone, so the only options are twenty and up.
The simplest tanks to use are aquariams, which are easiest and don't provide the risk of a gerbil slipping through the bars.
The waterbottle
Since gerbils chew just about everything in sight, it's important to get them a water bottle that they won't destroy. Usually the only water bottle you can get that they won't chew is a glass water bottle. I always keep two in the tank, and I recommend doing so, especially if they will be owned by children. Two water bottles allow for leeway when it comes to being a little forgetful. Ideally, you want both to be glass as they'll chew through the plastic lid of the water bottle, or a hard smooth rounded plastic which keeps them from chewing.
The house
Some sort of wooden house is necessary, we always have something like that in their cage for them to chew and sleep in. As rodents' teeth will continue to grow, they need to be able to chew something as hard as wood to keep them properly sized. I like to have two wooden structures in their cage at all times, both of which can function as houses in addition to chewing.
The wheel
All gerbils need a way to get out energy. If gerbils become bored, they can become unhealthy. Solid wheels are usually better than grated since their tail or feet can get caught in the grating as they run. As far as style goes, the better kind for gerbils is straight up and down, like the ferris wheel style, not the flat, flying saucer style. Flat wheels can be the cause concerning health problems. Best case scenario, gerbils will feel uncomfortable from an unnatural running posture, and won't use it, or worst case scenario, using it extensively may twist their spine over time and cause life-threatening health problems.
The bedding
Bedding is pretty simple. There are plenty of good options, many of which are soft beddings (paper, tissue, or soft woods) kiln dried pine shavings are also a good option, and what we use personally. If you're using a hard bedding, however, we recommend adding some soft bedding for their nests.
The sandbath
Sandbaths are good for their fur and their health as they're natural desert animals. It makes their coat shiny and gets rid of bacteria and infections. It's best to do this at least once a week, though it's not necessary. Just pour some clean, natural sand into a tub. Then place them in the sand. Depending on the size of their tank, you can keep the sandbath inside the tank and allow them to use it as they wish.
The Accesories
Accessories are important to keep the gerbils active, and entertained. This can be all sorts of things: wooden bridges, ramps, (simple) play structures, cardboard tubes or tunnels, even egg cartons and extra toilet paper, and paper towel rolls work well too. You can find all sorts of things around the house, but always be mindful that you're not putting any toxic in their tank since they will chew almost anything you put in.
