Before you buy any pet, make sure you have a home set up for them to minimize the stress of adjusting to a new home. If you are planning on bringing home a new hamster be sure to follow this list of supplies for what your hamster will need.
Get a cage that is large enough, escape-proof, and easy to clean. While the modular cages with tubes are fun, they can be difficult to clean and are poor on ventilation (and the tubes can be too small for some Syrian hamsters).
Never underestimate the ability of a hamster to escape, as they can fit through pretty small spaces and chew through plastic walls surprisingly quickly. If you are getting a Syrian hamster, keep in mind that many cages marketed for hamsters will be on the small side. If you are getting a dwarf hamster, be aware that they can often squeeze through the bars of an average-sized hamster cage.
Hamster Bedding and Nesting Material
Avoid cedar and pine-wood chips for bedding for your hamster. Aspen is a safer option if you want wood bedding, but many people prefer to use paper or other fiber-based beddings.
Hamsters love a cozy nest for napping, but the cotton nesting materials found a pet stores is unnecessary (and can cause problems if eaten or if it gets wrapped around their toes). Shredded toilet paper or facial tissues are an excellent nesting material (and are economical too).
Choose a good quality food for your hamster.
Pelleted foods offer a good nutritional balance and for many hamsters are a better option than loose food mixes. With a loose mix (seeds and other items), your hamster might pick out what they like and leave what they don't, which could result in a dietary imbalance (or an overweight hamster). A pelleted mix can be supplemented with a variety of other items, though, including fresh vegetables.
Hamster Food Dishes
A shallow, small, but heavy bowl (anything that won't be easily tipped over) is ideal as a food dish for your hamster. A small ceramic or porcelain crock are great options, as they are sturdy and won't be chewed up. You don't need to get fancy and buy a special hamster dish, but make sure whatever you choose won't be chewed up the next day.
Hamster Water Bottle
A small hanging water bottle with a stainless steel spout and ball is the most commonly used water container for hamsters. A bowl is too likely to be spilled, dirtied or filled with bedding, but you can offer both water sources for maximum hydration opportunities to your hamster.
Hamster Exercise Wheel
Hamsters love to run and need the exercise, so purchase the largest, best-quality exercise wheel you can. It should have a solid surface for running and ideally no cross supports (that might catch a leg or neck), so look for one that mounts on the side of the cage. Make sure the wheel is quiet as well, since hamsters run at night. A small amount of vegetable oil dripped onto the wheel axis may aid in keeping the wheel quiet.
Hamster House or Hide Box
Your hamster will appreciate a private getaway for sleeping. A house or hide box can be as simple as a small cardboard box (it will have to be replaced often but it is economical), a plastic hide box (it may be chewed up), a wooden box (it may be chewed or get soiled and smelly), or other things like a half coconut shell or a small clay plant pot.
Upside-down plastic food storage containers (such as a margarine tub) can be used if you cut out a door for your hamster.
In addition to a wheel, you hamster should have a variety of things to chew on and climb on. Plenty of hamster-safe items exist in the pet store, or you can use toilet paper tubes and tissue boxes to make toys for your hamster.