I think JOBO bottles would be the most convenient. They are very sturdy, are not prone to leak and are square, so they will fit very snuggly together in your backpack or a carry bag. I know that's what I would use. And yes, I would just pour enough stock into each one so that when I arrive all I have to do is to top them off with water, shake and pour into the tray or the printing drum. If you use stock concentrate, then even the temperature is of no issue since you'll be mixing with warm water on site.