buttplug - spend the money, hide it, don't try to use something around the house...it can get lost, and thats an embarassing trip to the ER

lubricant - for what? some body lotions will work, but, once again, I'd suggest buying it and hiding it

ping pong balls - they would work, they are small though, it would depend on the size of the mouth...they aren't strong for any sort of passionate bite

clit clamp - I'm not sure about that, but I'd say clamping the clit isn't something you want to do anyways, it's too sensitive, and you probably want it to stay sensitive, so just clip the labia and open it up