We find in the save folder (by default for Win 7-10 C: \ Users \ [User_name] \ AppData \ Local \ Daedalic Entertainment GmbH \ Skyhill \ Savegames) file Db.xml.
It has sections at the very beginning character and character_specs, in which you can change the maximum and current number of units of health and hunger, and the main characteristics such as agility, strength, etc. Below in the file you can find the section character_inventory, in which you can change and add items, edit their number.
I tried to make changes only to the started game, the file is updated when you exit to the main menu, but changes in the file are triggered only when the game is restarted.
Here are the names of some of the necessary items that can be added by analogy with the ones already in the inventory:
coin – coins for machines;
wood – boards;
glandules – scrap metal;
glue – glue;
brick – brick;
door_locker_1_item – pass;
door_locker_2_item – key
All item names can be found in the file itself.