I agree with the Ham radio and batery remarks but I disagree with the water advice for a few reasons.

1. Getting water sometimes is easier said than done. 1/2 liter isn't that much and will keep you going until you can find or secure more water.
2. In an emergency all water should be considered contaminated. If your not carring a micro-filter or Chlorine dioxide tabs your looking at boiling water. As most people don't carry microfilters, boiling and purification tabs are your only real opitions and they require time until you can drink anything.
3. Zip lock bags are great (I have 2 quart sized bags in PSK) but they only go so far. Having a real bottle can be a major plus if you've got the room to carry it.

Hope you don't take offence to my comments as that is not my intent, esp since I'm a new guy.