Considering you're a Garnier fan, you probably still some shampoo to get rid of the silicones or else no-poo won't work for you.
I'm not sure if the shampoos have silicones - my hunch is that silicones don't clean hair, so it's in the conditioners only. What type of shampoo is it? I can look up the ingredients online and see if it has silicones.
You can also just swipe some shampoo from somebody else in the house, or ransack your house for any shampoo samples (I know you've taken a few hotel samples, c'mon!).
Didja know that the silicones that make your hair look healthy and shiny may actually make your hair more dry in the long run? Some silicones actually keep water and moisture from getting to the hair shaft, so you are left with really dry hair, and it may be damaged or brittle eventually.
I really yucky thing that happens if you have silicones in your hair and you're finally clarifying it out is that your hair gets gummy temporarily. All the silicones soften with the shampoo and baking soda and it's all gooey
. After getting all the goop out, you will have nicely prepped your hair for no poo and have a clean slate, so to speak.