Found a fun little function that might be useable for Sandbox+"
character_add_prop([npc/player], [entry from items_3d.xtbl])
For example, this will equip the player character with the gasmask from the Zombie Attack mission.
character_add_prop(LOCAL_PLAYER, "gasmask")
I tested and it
does work, but
only in the Zombie Attack mission. I think that the item itself simply needed to be preloaded for it to work, so any of the normal items in items_3d.xtbl will probably work just fine in the open world. For the ones that don't we can probably pack them in one of the preload archives. I currently have my eye on the "avatar_wings" entry from m16 (the ones that matt's avatar gets when he starts flying around.).
NOTE: To prevent confusion, the gasmask prop that the above function equips is different from the actual wearable gasmask that is defined in customization_items.xtbl. What's interesting is that this particular function is only used in missions to equip props to npcs and never the player. For example, in the zombie mission, it actually equips the clothing to the player and not the prop. The prop is only equipped to Viola using the function. Yet, it still worked in my test for the player when using LOCAL_PLAYER as the first parameter.
I know a lot of you like to mess around with stuff, so feel free to experiment and post your results!