Bee here is an idea for a boiling water container that I carry in a wallet. It is a sort of super heavy-duty foil bowl.

Go to any mart or grocery store. They will have foil pans. Sometimes they are called oven liners at others they are called disposable cookie sheets. They are a large foil pan about 3 times as thick as as foil on a roll.

To start cut out a 12 1/2 X 12 1/2 inch square from the bottom.
Next cut out a 1/4 X 1/4 inch square at each corner.
Then fold the quarter inch stripthat is made along each of the 4 sides either once or better yet twice. This forms a rim that makes for a more solid pot. Fold these to the outside of the pan so you don'tform a dirt catching and holding area inside the pan.
Form a fold crease 3 inches in from the edge. Then unfold.
Repeat the same crease on all 4 sides.
This will form a 6 inch square in the middle that will be the bottom of the pot.
Then crease the 3 inch squares formed at each corner. The crease goes from the outer point of the corner to the corner of the battom square. When the sides are folded upright this crease foms a 45 degree flap from the base out ward to the top.
When the sides are in the up position these flaps are folded along the sides and tucked under the rim. This helps hold the pan more ridged.

This gives you a 6 X 6 inch square pan 3 inches deep. This gives a 108 cubic inches of pan. which is almost 2 quarts. Call it a quart and a half usable space since you don't really want to fill it to the brim.

To pack fold 2 opposing sides into the middle. A 6 X 12 package.
Then Fold the other 2 sides into the center. Now its 6 X 6 packet.
Finally fold it in half. Tis gives a 3 X 6 pack or roughly about the size of a dollar bill. Itwill tucks nicely in the bill compartment of a wallet. I have tested some in excess of a dozen times each. Because of the chance of wear and tear causing leaks not only of use but being sat on in the wallet I replace them about once a year. Hey they are cheap. I have yet had any spring leaks.

You do have to be careful moving them. The pressure of being nearly full of liquid can cause them to unfold. This loses the liquid and doesn't do much for the fire either. To clean unfold it completely flat makes it easer to wash.