Whatever problem is most important to your immediate survival, as opposed to your long-term survival and well-being. If you are stranded in a desert hundreds of miles from the nearest settlement with a week's worth of jerky and a single canteen of water, and the Baelrog has happened to take a winter vacation in your immediate vicinity and is looking kind of hungry, then the problem at hand is "how do I get away from the hungry Baelrog?". Worry about your 18-hour supply of water later, after you've distracted the Baelrog with half your beef jerky.