Without reagents, he can't cast any spells, but the spells he's capable of casting are things like freezing blasts of wind, firebolts, minor electric blasts, or summoning vines to entangle an enemy. Mainly spells based in the forces of nature, most often in what's available at the time. These spells are much more expensive in their reagent cost than most other spells, due to the hurried and wasteful nature of their casting, if he's using them to try to protect himself in an emergency situation. Most are rather weak though, not nearly as strong as if they were used by a mage of the same caliber as he is a witch.