Egg

Eggs are used to add viscosity and mouthfeel to cocktails, sour cocktails like Whisky Sour, tastes the best when made with added egg white. Egg whites create a creamy texture and a thick layer of foam on top of a cocktail. While unlike using just the white, adding the yolk adds a bit of a flavour to the drink, it helps emulsify the other ingredients and adds the eggnog flavour to your cocktail.
To get the silk smooth texture and mouthfeel and the foamy head without weakening the drink by melting the ice from too long shaking, which is needed to break the proteins of the egg white to froth up, dry shake the ingredients first, that is, pour all ingredients and the egg white in your shaker and shake hard without ice first, for about a minute and then add ice and shake again.

Port

Vinho de Porto as it is called in Portuguese, or simply Port is a Portuguese fortified wine produced in Douro Valley of Northern Portugal. It is sweet, thick red wine, headier than heavier than regular wine, and is usually higher in alcohol content than unfortified wines.

The production process of a Port is responsible for this higher alcohol content and sweeter and thicker texture. In the production of a Port, fermentation is halted before all the sugar is converted to alcohol and then distilled grape spirits are added to it to fortify it.

Port wine is now produced in many different regions and countries including Argentina, Australia, Canada, France, India, South Africa, Spain, and the United States, but under the European Union Protected Designation of Origin guidelines, only wines from Portugal are allowed to be labelled a PORT.

Port comes in several styles, which can be divided in two broad categories, wines matured in glass bottles and wines matured in wooden barrels.
Port matured in sealed glass bottles, due to lack of exposure to air, goes through reductive ageing, the wine loses colour very slowly and the resulting wine is smooth and bright red, while wood barrel matured port, has some exposure to oxygen due to the permeability of wood and goes through oxidative ageing, and they lose colour faster and lose some volume through evaporation too, resulting in a slightly viscous wine.

Ruby port is the product of a reductive ageing, and the process retains its bright red colour and full bodied taste, while Tawny Ports are ports made from red grapes that are aged in wooden barrels which end up giving then a tawny-brown or golden-brown colour. The flavour too is nutty instead of the fruity flavour of a Ruby.

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.

Milk

Milk can do wonders to your regular cocktail. For a rich creamy cocktail, milk does wonder .You may argue that milk as it is made of fat, and being low in acid, will easily curdle if its mixed with alcohol.
Best way to get a rich and creamy cocktail is to use bourbon, milk will soften its whiskey flavour. If you are looking for some spicier yet creamy cocktail go for Scotch with milk cocktails, they'll surely set you holiday mood.