Any item that was a plant or animal will compost. How easy and practical each item is to compost depends on many factors: what the waste is made from (sugars are easier to decompose than carbohydrates), size of pieces (small decompose faster than large). Waste is broken down faster at high temperature (X32 faster at 60C vs. 10C).
Consider the types of waste you add to the HOTBIN. Some types will compost down faster than others and consequently produce heat at different rates. When starting your HOTBIN it is advised to add lots of easy to digest waste.
We recommend that any large pieces of fruit and vegetables are cut up into pieces <4cm to speed up their decomposition. Add cooked food when HOTBIN is at 40-60°c internally.