I recently discovered this little gem in a store called Bolero. Basically they’re small sachets with powdered drinks with all sorts of sweet flavors to add to water. They’re gluten-free (seems obvious), sugar-free and they have 2 calories per cup of drink. Plus they have Vitamin C! It’s awesome!
You can buy a tiny 12-pack with different flavors and each one is enough for a liter of water. The smell is amazing, the taste is amazing, and it doesn’t contain sugar.
And of course I tried to combine it with Huel - you can clearly taste the flavor so it definitely can be used as a flavor boost!
Edit: It even has some unusual flavors for drinks, like lemon pie, chilli, panna cotta, carrot orange, vanilla, rum, cucumber, tomato, yoghurt, cola etc.