Keeping one-shot items in play?

[trekkie4life328]

One of our Munchkins insists that it is legal to keep one-shot items such as the Med-Kit and Mind-Control Gas, in play in front of them. They feel that once they are in front of them (in play but not in combat), they can still be used during a combat. Their belief is that the bonuses of this strategy are that you can have more items, but then everyone can know what cards they have.