First, you need enough volume in whatever cookware you have in order to cook the amount of food you're going to need for who will be there. This is also dependent on the kind of food you like to cook, and your appetites.
Second, it needs to fit into a certain weight category. If you're going to be walking for 4 days, carrying around cast iron cookware will become too cumbersome, making your abandon it along the way.
Next, it should be as compact as possible. Most kits nest together.
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For a trip for two people, consider getting a "two-man" set. These are compact, with the pieces nesting inside together. The lid can be used as a frying pan, especially if you have a detachable handle (pot grabber). They usually have two small bowls, which is really the only dish you need, besides a cup.
You also need a coffee pot, good for boiling water for tea, instant soups and oatmeal, and yes, even coffee! There are a lot of kinds available.
Each person would also carry their own cup. Some people hook it on their backpack to have it readily available at any moment during the hike.
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For a trip with more than 2 people, just add more two-man kits and a frying pan or two.
Titanium is a good kind of cookware as it's very light to carry but it's very expensive. Aluminum will do in a pinch but it tends to leak toxins into your food. Stainless steel may be your best best.
The kits that are made for girl scouts, mess kits, are ok. I've had mine for a long time, and after a lot of uses, flaked apart.
Just keep in mind:
- volume (enough room for what you'll be cooking)
- weight (make sure you can carry it!)
- compactness (you don't want to use a whole backpack to carry it, and not have room for food, clothing, first aid, etc.)