Hey dead head jed!
I have an "AmazonBasics" 24 sheet cross cut paper shredder that I got used a while ago. The strips are around 1/4" x 1.5". There are always a bunch of super cheap paper shredders here on Craigslist. I've been shredding newspapers and brown cardboard, so these cakes were a mix (mostly cardboard for the earlier ones and newspaper for the more recent). I've been discarding the outer layers of cardboard boxes before shredding them since those seem to have some kind of waxy coating. Not sure if it's a problem.
Here are the two types of lids I was using for this. The mason jar one is a lid with a hole in it put on upside down, with a filter disc on top, and then the band over everything. The one for the plastic containers is a small filter disc glued over a hole with silicone adhesive. The hole shouldn't be too big, since the mix is prone to drying out.
The kitchen scraps were all vegetable trimmings. Don't remember exactly what they were, nothing weird though. I just put them in the blender and added water until it would blend.
I cooked the smaller cakes (the cardboard + flour ones I posted first) for 45 minutes at 15psi. The bigger ones with the kitchen waste I did for one hour at 15psi. I imagine you're right that it'd be fine with less!
The two challenges I ran into were keeping the mixes fluffy and making sure there was enough water so it won't get too dry. Bigger cakes might be more forgiving with this mix, actually. Some of the 1/2 pint and smaller were pretty dry.
I think there's nothing super special about these cakes. Seems to me that pretty much any mix will work as long as it's fluffy, has enough moisture, and is made of things that the mycelium can digest. Vermiculite + BRF is an easy way to get there, but I imagine a lot of stuff around the house would work just as well.