4. The essentials
Have at least one easy-to-make cocktail up your sleeve and ready to go beyond a G&T. Maybe you enjoy an Old Fashioned or Cosmopolitan? So make sure you're trolley is stocked with the liquor and mixers you can always revert to.
Bases - Are you a screwdriver or martini fan? You'll want to invest in a good vodka. Margaritas? Then find a tequila that's 100% agave to avoid those hangovers. Finally, rum if you enjoy daiquiris or mojitos and bourbon for the Old Fashioned.
Mixers - Once the bases are on the trolley, start with the mixers. Anything from an elderflower liquor for sweet notes or Cointreau for orange flavoured notes. And of course, the obvious ones like tonic water and soda.