If you are looking for an accessible bottle that you can pick up at any standard supermarket, white rum (light or silver rum) is your best and most natural choice.
To understand why, it helps to look at how these spirits are made. Cachaca is a Brazilian spirit distilled directly from fresh fermented sugarcane juice, which gives it a grassy, earthy, and slightly vegetal profile. Most standard supermarket white rums are distilled from molasses instead of raw sugarcane, so they tend to be slightly sweeter and rounder, but they share the same sugarcane heritage. When you substitute white rum for cachaca in a caipirinha build, the drink is traditionally known as a Caipirissima.
Another very common supermarket alternative is standard unflavored vodka. Substituting vodka creates a drink called a Caipiroska. This variation is actually widely enjoyed in Brazil and is exceptionally forgiving, as neutral vodka lets the fresh lime oils and sugar shine without clashing with the fruit.
To make your drink with either substitute, keep the classic caipirinha method: cut a fresh lime into wedges, muddle them thoroughly in a sturdy glass with two teaspoons of granulated sugar to extract both the juice and the fragrant oils from the peel, add two ounces of your white rum or vodka, top with crushed or cracked ice, and stir well.
