You don't need to stock absolutely everything. Guests will be still able to find something to enjoy as long as you've got the basics right.

Depending on where you've ordered from, most shops let you return unwanted stock. If you have the budget, stocking an extra case of beer or a bottle of gin can ensure you don't run out, while not costing you anything if unopened and returned.

This really is the most important ingredient. Get plenty, as it's cheap and needed for almost everything from cooling beers to mixing in your G&T's. Drinks aren't the same without it.

Most ice will hold well enough for your event inside a cool bag or cool box if freezer/fridge space is at a premium.

Cups: Guests may average 2 drinks per hour, so you'll need at least 1.5 cups per guest, per hour.  This accounts for some guests accepting beers/ciders straight from the can or bottle. 100 guests might use 150 cups per hour.

Paper Straws: You'll only need half as many straws to cups. Not everyone will request a straw. 100 guests may need as few as 50 paper straws per hour.

Beer

Sometimes only around 30% of guests opt for beer as their main drink. It often depends on the crowd and type of event. Events can average out at just 1 beer per hour, per guest, with the majority of beers being drunk at the start of the event before people switch over to spirits. It's good to have them pre-chilled and ready to go but not to panic if supplies are dwindling later on as the pace will slow.

Less is more. Stick with a lager and a pale ale. My experience has taught me that many people prefer not to mix their beers. Fewer choices means you can have more of one type chilled down and ready to serve.

Cans are widely expected these days. They chill down faster and are easy to dispose of at the end of the night.

For simplicity you can serve in the can or bottle directly.

Cider

Cider is optional. It's the lesser chosen of the two drinks. If you do stock cider then stock less half the amount to beer, unless you know you have a cider heavy crowd.

Each bottle has 5 servings

Red or White?

It's often 40/60 mix. While red can be preferred in cold weather or when pairing with a certain dish; white wine typically wins out. You can usually opt for 40% red and 60% white when stocking up.

Table Wine

Allocate your table wine before thinking about wine behind the bar. Sometimes only around 20% of guests stick to wine after a sit down meal. 

Stock enough wine for your meal and then assume quite a few guests will switch to spirits after they've eaten.

Some tables will have wine left over and that can then move behind the bar as well.

If on a budget, allocate a quarter bottle of wine per guest when seating them for a meal. You can also keep some spares nearby and take it over when needed. This can be a good way to introduce yourself to the table if you've yet to say hello.

Behind the Bar

As mentioned, I see less wine served over a standing bar than many other drinks. However, it's still a good idea to allocate something for behind the bar. Stick to the 60/40 split and assume you might have around 25% of guests opting for wine vs spirits and beer.

Rose & Sparkling

Rose or Sparkling can replace of some of your white wine stock (and you don't need to stock rose or sparkling if you don't want to) as they have a similar flavour profile to white wine. Sometimes it's best to keep things simple. Factor in the style of your event and the time of year.

Each 70cl bottle has 28 servings (14 doubles).

The main spirits are Gin, Vodka and Rum (in that order). You may then wish to add some Whiskey. All other spirits should be considered optional, unless they are required for cocktails.

If 50 out of 100 guests drink 2 spirit drinks per hour, that's 3.5 bottles per hour, mostly split between gin, vodka and rum. A few will take whiskey. 

From the above we could suggest that 1 bottle of gin, rum and vodka (plus half a bottle of whiskey) per hour would be your minimum. However you'll really have to consider your guests and the type of event you're hosting.

This is a hard one to predict and you should take advantage of being able to return unopened bottles where you can. In this regard it can sometimes be more viable to buy bottles individually vs by the case. Keep your receipts and over stock.

Each 70cl bottle has 28 servings (14 doubles).

Wow there's a lot of gins out there. This is a category where you can really have some fun if you choose to. When in doubt, Gordon's or Tanqueray are staple choices that work in all situations. Just remember to supply 4 Litres of tonic to every 1 70cl bottle of gin and some sliced lemons for garnish.

Each 70cl bottle has 28 servings (14 doubles).

One type of vodka will suffice. Smirnoff Red is my go to but for the most pat people will be happy with any brand. Vodka will most likely be paired with a mixer like lemonade or cranberry juice. A sliced of fresh lemon is the most common garnish.

Each 70cl bottle has 28 servings (14 doubles).

Spiced rum is the most popular of the three better known rum varietals (Dark, Spiced, White). It's safe to stock only spiced rum, however you could add a bottle of white/light rum if you know guests will ask for it. Most common pairings with be rum with cola and a fresh lime wedge.

Each 70cl bottle has 28 servings (14 doubles).

Unless you know your guests specifically prefer Whiskey then I recommend stocking a much smaller amount vs the other main spirits. Assess your crowd but Jack Daniels is a popular choice to mix with cola and Irish or Scottish whiskeys may be requested neat. Ginger ale is also a nice pairing for a variety of whiskeys.

Each 2 litre bottle has 12 servings.

Coca-Cola: Stock more diet than you do regular. It's cheaper and it's the more popular choice right now.

Lemonade: 6x2 litre bottles of regular lemonade has got me through most of my events to date. 

Soda Water: You don't need much but a few bottles for the vodka & soda crowd are a must.

Ginger Beer: I'ts optional but there's often a few who'll take it. A handful doesn't go a miss.

Tonic: Match the amount of tonic to the amount of gin. The ratio is 4 litres of tonic to 1 bottle of gin. You'll have some tonic left over if people opt mainly for double shots.

Juice: I've never really needed more than a 4 pack of orange juice and a few cartons of cranberry (for vodka cranberry). Your mileage may vary. Any other juices are optional.

Others: Consider squash for the kids. Some sugar free alternatives if any guests are sensitive to sugar. Elderflower cordial and soda can be a nice addition.

Water must be available when serving alcohol. That's just the rules.  There will come a point in the night where everyone wants (or needs) a cup of water. If there's no tap nearby, stock plenty of bottles. If it's a hot day, stock plenty more. Don't mess about with this one.

Don't want to do the maths? I sure don't. These tools make planning your party bar super easy.

My top pick is The Knot's wedding planning spreadsheet. You can adjust drinks percentages and it gives you a clear breakdown of what to buy. Just load up the spreadsheet and head to the 'Drinks Calculator' tab. Download it here for Microsoft Excel or Google Sheets: www.theknot.com/content/wedding-planning-spreadsheet

Majestic party planner is another great tool. Not only is Majestic Wines a great place to order your drinks from but you might qualify for free glassware hire too. Here's the link: www.majestic.co.uk/services/parties