You gotta hand it to 7-Eleven for their environmental awareness. I just bought one single bottle of Singha drinking water and they didn't double bag, I just got the one plastic bag and two straws, which - If I ever did feel the desire to drink my water through a straw - would be lost inside if I let go, being as the straw (and it's spare) are two thirds of the length of the bottle.
Anyway I did my bit for the environment... As always I removed the bottle of water and left the store leaving the bag, two straws and reciept on the counter for them to put in the bin.
I will refill the bottle at the refill machine downstairs for a baht and a half and my only waste will be the plastic cap seal and my eventual wees.