Some of my friends began doing that this past summer, after exams. Some of them bought giant 2 litre glass beer boots to drink from and would buy a bottle of gin and empty the entire thing into said boot. They then topped up with tonic water. Sometimes they'd use lemonade instead but usually tonic. Then after consuming most of it, we'd go out and save whatever was left for next time - or when we got back. If we bothered to even go out, sometimes we'd just keep having a good time there.
I discovered that Rubicon: Passion Fruit or Mango hides the taste of alcohol amazingly well, so was resorting to that with vodka.