No frying pan or kettle to boil water in, no problem if you have rocks. A word of caution, however, certain rocks when heated can explode. They explode because of high moisture content. The moisture is trapped inside the rock and high heat will turn it to steam, and when the pressure builds it must go somewhere, and so you may end up with some jagged and very dangerous flying projectiles.
A Short Geology Lesson
As most of you know, not all rocks are as dense as say granite or marble. The less dense the rock the more likely it will be porous and permeable, in other words, oxygen and water can enter the rock. When the moisture in the rock is heated, it, of course, expands and can burst carrying fragments of rock along with it.
In scientific terms, there are three types of rocks, and they are sedimentary, igneous, and metamorphic. Sedimentary rocks, as the name implies, are the result of many layers of sediment from oceans and lakes settling on the floor of an ocean or lake. This build up can take tens of thousands of years. Igneous rock is volcanic and this very dense rock is created from hot lava, which cools to a solid. Metamorphic is a morphed rock if you will, which means that it either was igneous or sedimentary, but was heated, and then compressed over time, making an extremely dense rock.
Granite, marble, and slate are the most common hard rocks that would be suitable for cooking or heating to a very high temperature and the most available ones as well. Lava rock can be used, but getting your hands on some out in the backcountry could be a problem.
Granite and slate would be more readily available. Sandstone and limestone are everywhere, but if heated to high temperatures they will fracture and their porous nature makes for a very poor cooking surface.
Rock Frying Pan
A small slab of granite can be heated directly in the fire, and once well heated you can pull it aside and use like you would any hot frying pan. Use some fat from your meat to grease the surface and start cooking. Some high-end restaurants actually cook steaks, seafood, and other foods on hot rocks and then they bring the very expensive ensemble right to your table.
Gourds can be your kettle to boil water in or to make stews, broths and so on. A hollowed out pumpkin, for example, can be used by filling with liquid and then simply drop a number of hot rocks into the liquid until it steams.
Rocks used for boiling water are smaller rocks, of course, and make sure they are dense enough to withstand the heat of the fire. You can boil water for purification using this method as well.
A plastic lined ball cap can be a water receptacle in an emergency as well as a plastic lined depression in the ground or you can find a rock with a large enough depression to use as a bowl. Simply drop hot rocks into the water to the point you get steam rising.