lucky for you, LUA scripts are easy to implement.
Just go to your data folder. there find folder globaevents, then there should scripts folder and open startup.lua file
on that file you add the code inside the function and logic like i mentioned before is quite simple.
Just create 2 positions parameters one for 1 corner, another opposite corner. (aka map corners)
Then with this you can create table of entire map.
then loop trough each position and check for tile, if exists loop trough all the possible containers you want to have something in it.
check if there is something, if not. you can create randomly some items from list of itemID table you created for this.
and that is it.