Thanks to Rhys Cadwallader's recommendation of pineapple fizzy drink, I started experimenting with ways to mix it for other delicious non-alcoholic drink options. This one is my favourite:
I've named it "Lava Dream" in honour of this weirdly cute video about volcanoes that someone uploaded onto Wiztube. You could add rum to this drink if you wanted it to be alcoholic, but I think it tastes great as is.