TRAIN SANDWICHES (A Good Party Idea)  For each serving, split a hot dog bun horizontally, or for small children 1/2 a hot dog  bun or small dinner roll may work best. Fill with cold cuts or any favorite sandwich filling. Place sandwiches end to end. Use carrot rounds, or cucumber rounds as wheels, using 4 for each sandwich "car."  These may be secured with toothpicks if desired.  The first "car" or "engine" can have a carrot or mushroom smoke stack and 1/2 a sandwich placed on top. It is best not to make sandwich more than 1 hour in advance. Place a damp cloth over sandwich to keep it moist.