It's not What it Looks Like

I have definitely NOT guzzled down 4 bottles of Grolsch!
For starters, I don't drink :-)
These bottles sat in a box on the counter of one of the OpShops I visited today. When I asked the lady at the counter if they had been processed yet she said no and they wouldn't go in the shop anyway because they are alcohol bottles, which the shop doesn't sell. But if I wanted them I could have them for a donation. I agreed to the $1 donation she asked for, yes, one dollar!
What do I put in these bottles you ask? My home brewed kombucha ;-)