Garnishes

Garnishes include things like fruit wedges and onions.

Lemon slices
A good supply of lemon slices is a must.Generally a slice of lemon is added to gin and tonics but can be requested for various other drinks.

Lemon twists
You should cut up at least one peel for lemon twists at the beginning of each night.
Generally, you won't need many more than a peel's worth if that much. You should keep a few lemon wedges around as well, for the occasional lemony-fresh patron.

Lime Wedges
Cut your wedges from a Persian lime, the most common type, not a key lime which is smaller and yellower. The reason for this is because while they are similar, two different flavors are produced.
Always keep your limes refrigerated to ensure the customer, or friend for that matter, is getting the best quality lime. Also, cut the limes as you need them, not before hand. Unless you know you are going to need a lot, cutting them fresh is a must.

Cherris
Use stemmed maraschino cherries, because they're easier to get out of the glass; some bar patrons may also enjoy tying the stems in knots inside their mouths. Do not get cherries soaked in rum or other alcohols; make sure your cherries are alcohol-free, as even small bits of alcohol can be extremely dangerous for drinkers with alcohol allergies.
Keep a lot of cherries around.

Orange Flag
This is a cherry speared onto an orange slice. A "sex on the beach" uses this garnish as do many other mixed drinks.

Olives
Olives will be familiar to anyone who's seen a cartoon with a character drinking a Martini; or for that matter, anyone who's drunk or made one. You should keep olives that are green; pitted; and without pimento, the little red thing that you may find in some olives.
If Martinis are very popular at your bar, you probably really want to keep a lot of olives around, at least if you want to keep a lot of customers around.
Now it is common to have olives stuffed with different cheeses, such as gorgonzola, bleu cheese, and provolone. Also jalapeño stuffed olives are gaining popularity in the southwest region of the United States.

Onions
Small cocktail onions, the size of marbles, are used for Gibsons. Not many people order Gibsons; you should make sure you're prepared, but not over prepared.

Orange Slices
Orange slices are another popular garnish.

Mint Leaves
Mint leaves are required to make certain mixed drinks such as a Mojito and a Mint Julep. Mint leaves should be fresh, wrapped in a damp papertowel and refrigerated.
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