Bartending/Mixers

Mixers are non-alcoholic ingredients in cocktails. Mixers include things like grenadine, soda, non-liqueur syrups, and juices.

Carbonated mixers and sodas

Carbonated mixers are based on carbonated water. Due to certain properties of gas-liquid solutions and gas solubility, carbonated water does not stay carbonated for long; it quickly goes flat. Because heat decreases solubility of gases, and because an open container allows the pressure on top the solution to stay below the vapor pressure of carbon dioxide, you should always make sure carbonated mixers are kept in a keg or cold, closed bottle.

For soda fountains and soda guns (automated soda fountains), carbonated water is mixed for soda, colas, and tonic water by passing water through syrup and introducing carbon dioxide gas into the line from a pressurized tank. This ensures that the carbonation is always fresh, not weak or flat. Kegs usually come with a pump to allow them to be pressurized; you can purchase small pumps to replace soda bottle caps for the same reason, but they're rarely worth the effort except for very rarely used bottles. Remember, gases evaporate from water under low pressure; high pressure fixes this.

For carbonated mixers in bottles, try keeping smaller bottles for mixers that are used slowly throughout the night; use bigger bottles only for really popular mixers that run out fast. In either case, try to keep the cap on when not in use.

Juices

Whenever possible, use fresh squeezed citrus juices. These juices degrade quickly after being squeezed, and cocktails will not have the expected flavour or balance with sweet and sour mix or commercial bottled juices. For less easily made juices such as pomegranate or pineapple, the drink recipe is likely balanced for bottled juice, so feel free to use those, as long as they are 100% juice without added sweeteners or artificial flavourings.

Cranberry juice
Grapefruit juice
Lemon juice
Orange juice
Pineapple juice
Lime juice: Lime juice is one of the most common juices found in classic cocktails, as its tart flavor is very effective at balancing sweet liqueurs like triple sec, and its character has a natural synergy with the aromatic botanicals of dry gin. If used in a cocktail without a sweeter liqueur or juice, it is often sweetened with a small amount of simple syrup so as not to be unpleasantly tart. Lime juice is also a bit inconsistent compared to other citrus juices, so one must be sure to taste a cocktail and balance for it before serving.
Rose's lime juice: Rose's is a lime juice cordial, with sugar and preservatives added. It is a very specific flavor, which is often specified in Gimlet recipes. However, given the current availability of fresh limes in most parts of the developed world, it should never be substituted in recipes calling for "lime juice", only those calling for lime juice cordial or Rose's specifically.

Syrups

Grenadine
Peach nectar
Simple syrup
Orgeat

Bitters

Cocktail bitters (usually called just bitters) are highly concentrated liquids with a strong bitter flavor. They are used as a flavoring agent in small quantities of drops or dashes. Though they are typically made with an alcohol base, they are not intended to be drunk on their own and are usually not considered an alcoholic beverage. Cocktail bitters should not be confused with bitter liqueurs such as Campari or Chartreuse, which are considered alcoholic beverages and can be drunk on their own. Though there are numerous formulations of bitters with a wide variety of flavors, the three most commonly used in cocktails are:

Other

Cream
Ice
Milk
Water
Egg White