Visit a decent shop, and the amount of bar equipment is vast. But there are only a few things you really need, aside from alcohol:
Shaker. It is possible mix a cocktail in a jar or a jug, but since presentation is part of the pleasure, everyone should own at least one decent shaker. You’ll find plenty of opinion divided on the Cobbler versus the Boston shaker. The difference? The Cobbler is the classic three-part shaker with the body, strainer and cap. Bar aficionados dislike the built-in strainer as it clogs with ice too easily, but a classic stainless steel Cobbler looks good in your cocktail kit. The Boston is the glass and steel two-part combination that professional bar people seem to prefer – probably because the customer can see the drink being mixed as they shake. You can also use the glass part for stirred drinks, without it chilling in the hands as much as the base of the Cobbler.
Occasionally, one also comes across a third type – the French shaker – which is pretty much just a Cobbler without the strainer top. It is apparently gaining popularity in the US.
Measure. Accurate measure are important if you want to mix drinks consistently. A good barperson can pour by counting, using a pouring top, but for the rest of us, a drink measure is invaluable. The simplest is the double-ended type: the larger cup holds around 50ml (a jigger) and the smaller, 25ml (a pony). The problem with these is that as you flip them over to use the ends, you get drips of the previous measure everywhere – better to buy a pair of small measures, if you can.
Bar Spoon. Simply, a long spoon for stirring drinks. Real bar spoons have a spiral handle that allows you to rotate them between the fingers, as a stirred drink should be treated gently. Any long-handled spoon will do, but I would avoid the cheaper spoons that have a spike under a rubber cap. I assume these are to get olives or cherries out of jars, but the cap seems to disappear all too readily. Likewise, versions exist with a flat plate on the end, presumably to be used as a muddler; really, they are too lightweight to be used for this.
Strainer. To use a Boston or French shaker, a strainer is essential. The Hawthorn type is the bar standard – a pierced plate with a number of prongs that allows is to be rested flat on the rim of the shaker. A spiral spring around the edge of the plate filters out the coarser lumps of ice or fruit, but allows some small pieces through.
Muddler. To get the flavours out of some ingredients, like citrus zest in the Old Fashioned, they need to be crushed to release their oils and juices in the glass. A heavy spoon would do this, but the best tool is a muddler, which is simply a short length of a thick wooden dowel, somewhat like a miniature baseball bat. Available in various lengths, one around the 8″ (or 200mm) mark seems to be the most useful.
Paring knife. Garnishes are a big part of a drink’s presentation, and cocktails like the Old-fashioned really benefit from a large slice of orange peel being spritzed over their surface. To prepare slices like this, you need a good, sharp knife – either with a straight or curved blade. The brand I prefer most for this is Opinel: the blades are just the right length, and sharpen beautifully.