For trolleys and locos:
http://www.harborfreight.com/1...case-69318-8538.html
http://www.harborfreight.com/1...inum-case-62272.html
My freight cars are mostly of the $5 variety, so I stack 'em in a gym bag and call it good.
More delicate freight and specialty cars get carried in their original factory boxes when feasible, or an appropriate-sized cardboard box as needed.
Mitch