Large pieces of ice tend to melt more slowly when submerged in liquid; especially under normal temperature conditions. In other words, if you want to delay the effects of dilution in your spirit or soft drink, invest in a bigger ice cube rack.
The plastic ice rack that came with your fridge probably makes smallish ice cubes. Thankfully, it's pretty easy to find large silicone replacements that won't take up too much room in your refrigerator. In addition to making your scotch look manlier, larger ice cubes also take longer to melt.
Now, before some smartass mentions it in the comments, we're fully aware that the chilling power of ice mostly comes from the dilution process (aka enthalpy of fusion). However, a stack of iceberg-sized chunks will still help to keep your drink cool without flooding it with extra water.
Plus, smaller ice cubes tend to congregate at the drink's surface, which can lead to a sharp increase in surface water. They also allow you to fit more liquid in the glass, which is bad news if you're trying to cut down on sugary soft drinks.
So in conclusion, while large ice cubes won't keep your drink as icy-cold to begin with, it will taste a lot better and continue to clink pleasantly. Hurrah!