My half scale cake bodies (the clay) were mainly cut out to shape used color pen's cap (which is bigger than regular pen's cap) - no other mold, cutting tool or cookie cutter. So, the thicker clay layer made out nice dome shaped body. For heart shape and square shape cutters, I used metal strip from plastic food wrapping package and bend it into shape, not a perfect curve, but it works! The most time-consume part is pearl making, I roll small portion of clay into tiny ball. It's not that easy (for me) to make similar size tiny balls. And so, before I get enough pearl to decorate a cake, my fingers hurt!
It's amazing that every time I start making new cake, new idea just pop up into my head what around me to be used and so far, I do not need any special tool to make my mini-cake at all.
Now, just have a look around and try to figure out how could things you found can be used for your miniature. ;)