I’m not suggesting you try this at home, but the main substance used to pack the cleaned organs and body was natron; a combination of sodium carbonate and baking soda.
A simple marinade of wine and spices was used to clean the removed internal organs.
While oil, another common kitchen staple was used to rinse residues out of the abdominal cavity - the variety was probably cedar.
Next we might have to raid the laundry for wads of linen to stuff under the skin to plump out sunken cheeks.
From outside yards we could scavenge sawdust or mud to top up the body’s cavity (tar was another favourite).
The entire contents of the linen cupboard might have to be sacrificed to wrap the Mummy in multiple resin soaked layers. Looting the jewellery box would be our next step as precious gems and magic amulets were often inserted inside the linen layers.
Stretched out these bandages could measure 2.5 km!
The Ancient Egyptians believed their ka (spirit) required their physical body so they mummified it to last forever.
It’s an interesting concept and one I explored in Golden Scarab with the High Priest committing a sacrilege not only against the physical body of his foe, but stealing his afterlife. Does he get away with his crime?