I heat water in my one kettle (600 ml titanium). Most of it goes to rehydrate my food (in a freezer bag inside a cozy). I drop a tea bag into the remaining hot water for my hot drink. No dishes to wash!

Of course that won't work if you cook your food in your pot. Some like to put water in the pot (after eating the food), and heat it up for a beverage, which does help to clean the pot, but I personally don't like rice or noodles floating in my tea!

It sounds as though you want a cup you can heat water in. Titanium is far lighter than stainless steel, probably half the weight. There are a number of various sizes and shapes on the market. They are more expensive, but last basically forever. Aluminum is almost as light, but getting hard to find (due to the popularity of titanium) and is apt to get dented and be useless in a couple of years.