[MunchkinMan]

It's a little from column a, a little from column b, with respect to putting Items into play. You can put Items you can't use in to play, but you are not required to do so as soon as they hit your hand. Until the end of your turn, you can have any number of cards in your hand, so if you are over the limit, you can certainly empty your hand of Items you can't use, as well as one-shot Items, by putting them into play. Remember, one-shot Items can be used from your hand or from in play. As long as you put the Items you aren't using sideways, that's all that matters.

And, yes, cards never return to your hand without that ability being expressly given by a card. There's no rule in the rulesheet that would allow for it, so it would have to come from a card.