Breath fresheners are easily portable and will mask odors in your mouth. Sugarless gum will help stimulate saliva production. Saliva is a key factor in helping the body rid itself of odor.
Some personal care companies have also started manufacturing disposable toothbrushes. A product like the Colgate Wisp brush, a tiny brush that helps dislodge food particles while freshening your breath, is a discreet way to clean your mouth on the fly.
When all else fails, use your secret weapon: water. Simply swishing water around in your mouth will help remove unwanted food from in between your teeth and prevent smells from happening before they start.