I found the menu to change whether events happen, personality traits, remove loot items.. but didn't see how to add new loot/starting items. Thanks.
do you mean the scattered resources at the beginning of the game, like meals and clumps of steel?
That's the 'Scattered' option when you hit the add button
Senario editor-edit mode-add part-start with-Choose the thing to start with.
Hope this whas what you need.
there are three different choices with that there is the Start with which allows it to come down in a droppod with your colonist. There is also Start Near which puts the items near where your colonists come crashing down. (an example of that one is the wood you find and use to build with. And lastly there is the Scattered randomly Which is like some of the survival meals and steal you find throughout your map.