Vodka

Vodka is an European clear distilled alcoholic drink that has been one of the most popular drinks across the world .

You'll find it to be the most popular spirit in drink making because of it's neutral taste and absence of flavour and colour.

Vodka often replaces Gin in many traditional cocktails

Vodka is known to be good for the heart, and if consumed in moderation, can prove to be good for cardiovascular health

Note that these days there are flavoured Vodka available in the market too, and some cocktails do make use of them.

Lemon Juice

Lemon Juice being rich in Vitamin C is an excellent remedy for sore throat and aids in digestion and controls blood sugar, and also promoted weight loss. It is used for various culinary and non-culinary purposes all over the world. Lemon juice is known to reduce or even reverse the effects of excessive alcohol consumption and intoxication.
In drink mixing, fresh lemon juice brings a tangy zing to so many classic drinks and in fact, it's the most used ingredient in drink mixing other than the liquors of course.

Sugar

Brown Sugar is a sucrose sugar with a distinctive brown colour from the presence of molasses, it is a partially refined or unrefined sugar containing sugar crystals and residual molasses giving it a distinctive taste and flavour of crystallised molasses or toffee. The taste of dark brown sugar is described as a caramel taste with a deep molasses flavour.
Brown sugar is used in cocktails where a caramel candy or toffee flavour is expected.

Caster Sugar is finely ground granulated sugar. It is not as fine a powdered confectioners' sugar and has a little grit to it. It is somewhere between confectioners' sugar and granulated sugar, and melts in mouth with a mild spicy feel to the tongue

Vanilla Sugar is the regular granulated sugar infused with vanilla flavour, by using vanilla pods and seeds to flavour the sugar. A home made alternative is to use vanilla sticks or pods in a jar of sugar and leave it sealed for 4 weeks to allow the vanilla flavour to infuse. Or to use granulated sugar and vanilla extract and blend in a mixer, although this ends up in powdered sugar.

Blue Curacao Liqueur

Curaçao is a liqueur flavored with the dried peel of the bitter orange laraha. It's been a popular liqueur for more than 150 years, the Dutch East India Company created this orange liqueurs by steeping orange peels in alcohol from the island of Curaçao and called it Curaçao liquor, unlike Triple Sec, Curacao has added spices and herbs to the orange and Curaçao comes in a variety of colours such as clear, orange or blue.

Blue Curaçao being the most used of them, in cocktails. Although Curacao is an orange tinted liquor, Blue Curacao is a regular Curacao dyed bright blue to give it a striking appearance, and thus is a very popular cocktail mixer, whenever a striking colour is desired.

Blue Curacao is usually around 25% ABV.

Blue Curacao is essentially Orange Liqueur tinted Blue, the colour doesn't influence the taste and thus Orange Curacao is interchangeable with Blue Curacao in recipes, if the colour is not important in the appearance.

NOTE: Blue Curacao being an Orange Flavoured Blue Liqueur, it's primary purpose in a cocktail is introducing the Orange flavour and the striking sky blue to the drink, so, if a bottle of Blue Curacao liqueur is something you are not planning to buy right now, you can manage with the Blue Curacao Syrup.
It would add the same flavour and colour profile to the cocktail, all we need to do is simply count for the alcohol absent in the syrup and account for it.