You might get a faster answer in the D&D 3.5 Rules forum instead of General RPG Rules...What skill would apply if a character were to try to smuggle something in a wagon or ship? In other words to hide something. Hide? Sleight of Hand?
I would probably let the player use hide. If he can hide himself, he should know how to hide other things too.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.