Empty trashbags can now fit inside backpacks. (#21888)

* i think this is workin

* sillly me

* also this guh

code/game/objects/items/weapons/storage/bags.dm

@@ -42,6 +42,31 @@
 	can_hold = list() // any
 	cant_hold = list(/obj/item/disk/nuclear)
 
+/obj/item/storage/bag/trash/proc/update_weight()
+	if(!length(contents))
+		w_class = WEIGHT_CLASS_NORMAL
+		return
+
+	w_class = WEIGHT_CLASS_BULKY
+
+/obj/item/storage/bag/trash/remove_from_storage(obj/item/I, atom/new_location)
+	. = ..()
+	update_weight()
+
+/obj/item/storage/bag/trash/can_be_inserted(obj/item/I, stop_messages = FALSE)
+	if(isstorage(loc) && !istype(loc, /obj/item/storage/backpack/holding))
+		to_chat(usr, "<span class='warning'>You can't seem to fit [I] into [src].</span>")
+		return FALSE
+	. = ..()
+
+/obj/item/storage/bag/trash/Initialize(mapload)
+	. = ..()
+	update_weight()
+
+/obj/item/storage/bag/trash/handle_item_insertion(obj/item/I, prevent_warning)
+	. = ..()
+	update_weight()
+
 /obj/item/storage/bag/trash/suicide_act(mob/user)
 	user.visible_message("<span class='suicide'>[user] puts [src] over [user.p_their()] head and starts chomping at the insides! Disgusting!</span>")
 	playsound(loc, 'sound/items/eatfood.ogg', 50, 1, -1)