Damn, I started answering this, and then one of my kids called me looking for footnotes to her excellent 9th grade paper on Philip Larkin's poem: "They ###### you up, your mum and dad" ( and our anti-poetic, puritanical censor will mess that up).
Basically, any carbohydrate and water mix, most commonly potato flakes nowadays, though some still use cornflour, will do. The tiny ff maggots don't eat it though. Instead they eat the microorganism that grow in any high carbohydrate mix which acts as a culture medium. Orin has a pretty good "sticky" at the beginning of this forum, which you should read. The only thing in addition to the water/potato mix (follow the instructions on the box and then add a little more water), is yeast. Most people sprinkle an inadequate amount of active yeast granules on top of the mix, and this is supplemented from yeast spores in the air together with microorganisms that they eat. There is a myth that some fermenting fluid, like vinegar (which in fact is sterilized and contains no agents of fermentation at all) promote egg laying, but its use is quite unnecessary. Brewer's yeast, though, contains ruptured yeast organisms (it is killed yeast. by product of beer brewing) and it is not a bad idea to toss in a cupful of that to five cups or so of potato flakes. I personally use a cup of it and 1/2 cup of active yeast to 6 cups of potato flakes. some of us have also experiment with adding a protein powdered like casein or milk whey to the mix, but this complicates the process and helps drive up the per unit cost, so I suggest that you stick with the flakes, water, yeast --if you just sprinkle on a little, it will start fermenting immediately -- and forget all the "extras like casein, apple slices, bananas, molasses (sorry Superfreak!) and the "secret ingredients " that some members swear by, The FFs can't read. They won't know the difference.
The reason, by the way, that most breeders just sprinkle yeast on top of the mix instead of mixing in half a cup full is that 1/2 cup of yeast will create a lot of carbon dioxide as it does in rising bread. I usually let it do its thing over night in a warm part iof the kitchen and then stir it (I use a stand mixer but a fork will do) to remove the carbon dioxide bubbles.
Finally, if you have a problem with mold in yr cultures, you might want to try an anti mold chemical or paraben (from, e.g. Josh's Frogs) or the one that Hibiscusmile, who makes more ff cultures than most of us put together, uses.
Good luck!