For the classic Irish preparation you will need:
Glass and spoon (obviously you say but the spoon is important!)
1 1/2 -2oz decent whiskey - Irish of course i.e., whiskey spelled with an 'e'.
Tsp of brown sugar
Slice of lemon
5-6 whole cloves
Just boiled water from the kettle.
It's rare the kitchen in Ireland without an electric kettle.
Stud the slice of lemon with the cloves.
It's rare the bar in Ireland in winter that doesn't have the lemons ready.
Mix the sugar with whiskey and pour in the hot water with the spoon in the glass - this helps not to shatter the glass. The more water you use the hotter (and weaker) the drink.
It's rare the person in Ireland who calls them anything but a hot whiskey (instead of 'toddy').