There are two natural options; none of them is quite pleasant.
Per Wikipedia, 8.5 vol% of ethanol make the freezing point drop to -3C (26.6F) (more values at at Wikipedia, also a diagram is available below).
Most of the ethanol will be evaporized during cooking, so it's not that much an issue; also 14 vol% is only 6.8 wt%, so the added weight is 6.8%, which sounds like a lot, but still it's 1/15 only. The good thing is that you can get cheap and quite strong alcohol almost anywhere around the world. Of course, this has some issues, such as where to get spare alcohol for a longer journey; also, some alcohol will be always left in the solution, no matter how hard you try, which is not good at winter.
Note that you can get a 90% alcohol at special shops, but it can get quite expensive because of the excise tax. Don't buy technical alcohol, it's denaturated, i.e. very disguisting and possibly not really safe to drink.
Note that you can't really do much with salts. The most efficient salt is NaF (sodium fluoride). However, it is poisonous, lethal dose is around 8g/100kg weight. We can compute that even a huge amount such as 34 grams of NaF in 1 litre of water reduce the freezing point to -3C. However, that's 3.4 wt%, which is freakingly lot.
For NaCl (kitchen salt), the amount to get to -3C is 47 grams, so almost 5%. Since the relationship is linear, any reasonable amount of salt has close to zero effect on the freezing point.
Do not do this. Find other methods how to supply yourself drinking water in extreme conditions.