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.
Step 2: 2. Prepare Your Firestarters
Here we’ve used egg cartons (recycled cardboard, not Styrofoam). Sometimes you’ll find molded packing in boxes made from the same cardboard material, so we cut out some hollow parts of that as well. Carefully trim off the tops and outer sides of the egg cartons with heavy kitchen shears or a box cutter. Fill the cups with cedar, pine, or hardwood shavings (like pet bedding or sawdust from a woodshop).
NOTE: Some people fill the cups only with wax, but wax is flammable like kerosene - it needs an organic wick to burn. Don’t worry, there will be plenty of wax left over to cover your wood (tinder and kindling). Stir your melting wax with a wooden popsicle stick or bamboo skewer.
Step 3: 3. Pour Wax into Molds
Use a hot pad or oven mitt, the wax container will be hot. It’s best to let the wax cool just a little bit, since very hot wax will go right through the bottom of the cardboard, while cooler wax will bind with the shavings and just soak into the cardboard. Pour slowly; better to go over it twice than over-soak and waste wax. For the example shown, 1 lb. of wax filled 2 dozen egg cups and 2 larger cups.
NOTE! Allow wax to cool at least half an hour before moving - otherwise you’ll have melted wax all over the place.
Step 4: 4. Cut Apart Egg Carton Cups
We used heavy kitchen shears, which are safer than a box cutter or sharp knife. Once completely cool, store your firestarters in a (waterproof) plastic zip food storage bag. To use, place one of these in the center of your tinder and kindling, so the wax melts onto your wood. If you build the fire over it, the wax is wasted, melting into the ground.