Lots of nice cordials around. Buderim ginger cordial. There are fancy schmancy elderflower cordials too. The Bickfords range is huge. My all time favorite is the Bickfords Lemon Lime & Bitters. I used to be a fan of Schweppes Lime cordial but I don't like the taste now - too fake sweetener and nothing like what it used to be 20 years ago.
You can make your own cordial by blitzing up a punnet of raspberries or blueberries with their own weight in water plus half to one third their weight in sugar (or a bit less), mix in a teaspoon of citric and/or tartaric acid. Bottle and keep in the fridge for up to a week. If it ferments, you now have alcoholic cordial .... Or go to YT for a recipie for raspberry shrub which is a vinegar based cordial and very nice indeed and possibly quite healthy. PS. Grenadine is a fancy very sweet pomegranate cordial. Kinda gluey, but essential for a proper tequila sunrise.

I'm partial to the Aldi Westcliff Fruit Cocktail cordial. I add a bit to the glass, then add the soda water.

Depending on how much cordial you put in, it goes from tasting like those mineral waters with 5% juice (my preference) all the way up to a full blown Passiona.

NB: I don't like the Aldi Raspberry Apple or Lemon cordial. For lemon (like a lemon squash), I like the Diet Rite Lemon with soda. Diet Rite Lemon, Lime & Orange is good too.

I think those cordials are about $3.50 a bottle, though. So if you just want a couple of bottles to drink for one night, you're better off picking a couple of bottles of the homebrand fizzies. Eg WW Diet Orange & Passionfruit is $1.10, and the same price as a bottle of soda water. I haven't had it, but it probably tastes about the same anyways.

I also didn't mind the Woolies Diet Ginger Ale $1.10/bottle, but haven't had that for quite a while. Lime goes well with it, but the real limes are often expensive. You can pick up a bottle of Lime Juice for $1 and give it a little squirt to add some more flavour.