Tonic water is the kind of provision you don't normally buy, but occasionally really need—and there aren't any real substitutes. Bartender blogger Jeffrey Morgenthaler offers a DIY recipe for making a clever substitute at home.
You won't be brewing your own quinine or high fructose corn syrup for this hooch enhancer, but you will need to find some ingredients that aren't available at the corner food mart. Allspice berries, powdered cinchona bark, and citric acid are the real stand-outs, but Morgenthaler helpfully provides a supplier link for at least the cinchona bark. Besides, if you're going to spend some time making this stuff, you'd probably want to make it in a big batch and store it—with perhaps a splash of vodka as stabiliser, if you don't plan on using it for non-alcoholic drinks.
Morgenthaler's recipe was picked up and photographed step by step by one crafty Instructables user, which is worth having hand when making your concentrate. If you know of another tonic recipe, or substitute, let us know in the comments.