If it was someone I cared about I would be offended to find a business card in their corpse's clothing and I would never call that person or do business with them. At a funeral you should be mourning and paying your last respects, not seeking business opportuntiies. If you really must be an opportunist in what is a sad event for most people there, it would be more tasteful to leave the card at the entrance. I doubt that people are worrying about looking for people to do business with when they are at the funeral anyway, so chances are you wouldn't get many callbacks even if it's a fantastic card...