[Andrew Hackard]

Summarizing the above, more simply: You cannot trade cards from your hand unless you play a card that allows this. You cannot trade non-Item cards from the table, either, unless you play a card that allows that.

Yes, playing one-shot Items to the table is allowed, either because you want to avoid giving Charity or because you want to dissuade people from working against you. One-shot Items can be played from your hand or from the table.