I'm going to show you how to make a 2 part mold out of everyday household items, MacGyver style. Keep in mind, this is by no means a professional level mold. It will be made by finding what we have on hand, and without buying anything.

For this instructable I used the following:

5-6 Plastic Business/ Reward Cards
A Pair of Scissors
A Hot Glue Gun and Glue Sticks
Scotch Tape
Vegetable Oil
Paper Towels
Elmers Glue
Microwave
Freezer
A Champagne Cork

Step 1: Creating the Mold Housing

We must first build the housing for our tiny mold.

Cut the cards down to a height and a width that matches your negative, while leaving enough space so the glue has room to fully encompass the negative.
Once you have these pieces, you can take 2 of the cards and cut them in half. This will allow us to create the two halves of our housing. You should have 2 long pieces, 2 short, and 1 square.
Begin taping the pieces together (as shown in the image above). Trim as necessary in order to accomodate the item you decide to use as your negative. You should end up with what looks like a medium sized matchbox.
When creating your 2nd half of the housing, simply repeat the steps with 1 exemption. do not attach a bottom piece. This will be become clear soon.

Step 2: Completing the Housing

Once you have all of your pieces cut and taped together, you should have something that looks similar to the images above. Except unlike mine, one of your boxes should not have a bottom. I fixed this mistake later.

Step 3: Creating the Mold: Part 1

Now that you have a housing for the mold, we can begin to create the mold itself. Now I will admit, Hot Glue is an awful, awful, terrible thing to use for making a mold. But I did it anyway. Don't Judge, I was bored.

Fill your bottomed housing with hot glue. Make sure it is HOT! It needs to be in its super liquid form or it wont work. So, don't be like me and try to use a low temp hot glue gun. It doesn't work very well. I would suggest using an industrial high temp glue gun. But because this instructable is based on house hold items, we will use what we have!
So I gave up on the low temp glue gun (for this part) and instead opted for something with more heat. The microwave! So, using your scissors, cut up 3 glue sticks into smaller pieces and fill up your housing.
Once your housing is full, place it in the microwave on top of a microwave safe plate or saucer. And heat "intermittently" for roughly 6 minutes. I varied my time by heating for a minute and checking the glue, heating for another 2 1/2 and then checking again, etc. Just be extremely careful not to over heat, as the plastic housing can melt, or even worse the hot glue can bubble or explode all over the inside of you microwave. And no one wants that kind of mess to clean up.

Step 4: Creating the Mold: Part 2

Once your hot glue is in a liquid state, you will need to place your negative.

Make sure you coat the negative in a releasing agent. I chose vegetable oil!
Place the coated negative into the hot glue but be careful not to press to far. The hot glue will poor out over the edge, so be careful not to burn yourself.
Once the negative is placed, you can put it inside your household freezer or refrigerator to help with the cooling process. Should take 5 minutes or less.

Step 5: Creating the Mold: Part 3

Once the 1st half of the mold has cured, take it out of the fridge. And begin work on the 2nd half.

Using our releasing agent (vegetable oil) cover the negative and the mold so the glue does not stick.
Place the bottomless housing on top of completed mold #1.
Using your hot glue gun, begin to fill the top housing until it is full.
Once the glue has cured (feel free to use the Fridge again if necessary) you may remove the the plastic housings and separate the two pieces of your now completed mold.

Step 6: Creating the Cast

Now that we have our janky little glue mold, we can begin creating castings! Yay!

First you will need to poke, or cut a hole in one side of the mold. This will be where we pour in our "resin."
Except there is no resin in most households, so I opted to use Chocolate, but that didn't work. So I switched to Hot Glue once again, but that didn't turn out so good either. Eventually I found a bottle of Elmers glue and BAM! Back in business.
Make sure to coat the inside of the mold with our vegetable oil releasing agent. So that the elmers glue "resin" doesnt stick to our hot glue "mold."
Bind the two pieces of the mold together using whatever you have. I was going to use rubber bands, but couldn't find any, so I opted for some string and a good old clove hitch. Make sure you have a tight seal, or you will end up with leaking from the seams of the mold, in which case you will need to continually add more "resin" to the mold as it solidifies.
Once the "resin" has been poured into the mold, place the mold into the freezer on top of a paper towel (in case of leaks). I left mine in for a few hours, continually refilling as needed due to the lack of a tight fit. This will only freeze the glue.