These are special item models, generally one of these types:

MDLTypeSpecificsNotes

gi_armor01

Engine HardcodedGround Armor Item: Cloth
gi_armor02Engine HardcodedGround Armor Item: Leather
gi_armor03Engine HardcodedGround Armor Item: Chain
gi_armor04Engine HardcodedGround Armor Item: Plate
gi_cloak01Engine HardcodedGround Item: Cloak
it_potion_000Engine HardcodedAnimation: Drink Potion (not also uses gui_potiondrink sound effect)This is also the ground item for potions in baseitems.2da - which don't have their own models so this usually spawns.
it_scrl_000Engine HardcodedAnimation: Read ScrollNote the actual scroll on the ground is gi_scrl as per below
it_bagCommon baseitems.2da and elsewhereUsed for most ground dropped items, thrown in spells.2da for caltrops (would be worth changing there tbh) and as a bodybag.
gi_wamar_001Common baseitems.2daArrows ground item
gi_wambo_001Common baseitems.2daBolt ground item
it_dart_000Common baseitems.2daDart ground item
gi_scrlCommon baseitems.2daScroll ground item