We've discussed people and vehicles for a layout, but one of the most effective elements of building your layout's character are little detail items.
You can find plenty of detail packs from Woodland Scenics, Scenery Express, Arttista, and of course Lionel and MTH. But many of my favorite bits are pieces that came with something else. You know, forklifts from factory kits, luggage carts from station kits, and things that might be left over from other items. Baggage carts from a damaged access...