Like your glassware, the mixers you'll want to have on hand can vary according to the style of drinks you intend to make. They're also an alternative for guests who prefer nonalcoholic drinks. While there are some staples to keep in your drinks cabinet, there's no shame in pretending you're fresh out of clam juice when someone asks for a Bloody Caesar.
Instead of stocking the more outlandish ingredients, keep an assortment of standard mixers that work as a base for popular cocktails. Juices are one set -- most bars have a standard set of four or five in the well and a ready supply of orange, cranberry and tomato juices. Throw in some sour mix and milk or cream, and you're halfway to making common drinks like screwdrivers and vodka cranberries. The other set of mixers is sodas. A soda gun is ideal (and is what commercial bars use), but for your purposes, assorted bottles of lemon-lime soda, ginger ale, cola, tonic water and plain soda water will suffice. Finally, for shelf mixers, there's Rose's lime juice, simple syrup and grenadine. Angostura bitters is another classic ingredient that's become rarer these days, but it keeps forever and having a small bottle available will impress old-school cocktail lovers.