Liquid for cooling beverages
If brine is either unpalatable or has too high a freezing point for you, other options include a solution of glycerol in water. Glycerol is perfectly safe to ingest in modest quantities -- it's used as a food additive and a medicine -- although it tastes a little weird (a bit like extra-sour sweet and sour sauce).

Although it's mostly been replaced by ethylene glycol now, glycerol used to see a lot of use as an antifreeze, and is still used in domestic applications like ice cream makers. Apparently it's best used in a 60-70% solution, when it can get a freezing point below -40°C.

The paper linked below puts the optimum point at -46.5°C with two-thirds glycerol, one-third water by weight.


"Freezing Points of Glycerol and Its Aqueous Solutions", Leonard B. Lane, Ind. Eng. Chem., 1925, 17 (9), pp 924–924, DOI: 10.1021/ie50189a017