These are old-fashioned Boy Scout waterproof fire starters, like I used to make as a kid (and Scout). I'm now in my 31st year of active Scouting, and I teach this to new leaders.
What you will need:
Stove top or hot plate
Double boiler, or a metal bowl that fits inside a pot
Cardboard (NOT FOAM) egg cartons
Wax - canning/sealing wax, old candle stubs, etc.
Some kind of small flammable material - wood shavings or sawdust, paper small animal bedding, 100% cotton dryer lint, etc.
Oven mitts, grill gloves, or hot pads
Step 1: 1. Melt Your Wax
ALWAYS use a double boiler for melting wax! This means 2 containers — a bowl or pot with your wax in it, which goes inside another pot or bowl with about 1” of water in the bottom. The bottom of the inner wax pot/bowl must not touch the bottom of the outer water pot/bowl. Why? This keeps the heat under the wax at the boiling point of water (212°F/100°C), which is plenty hot enough to melt the wax, but not so hot that it would cause a fire. NEVER melt wax in a single container on a burner, in the oven, or in the microwave. This step should always be done with adult supervision. In this case, we used a “hot plate,” which is a single stove-like burner we use for hobbies. You can use old candle stubs; in this case, we used Gulf Wax, available in the canning section of your store for sealing jelly jars.