Great ideas here, especially the increased inventory ideas.
Here's a few:
A single or multi-use item that will teleport you to a random spot in your current area.
A ring or cloak that will automatically cast Mage Armor (either using it's own spell, or triggering your mage's) when a mage is struck by an enemy. The effect is instant and affects the aforementioned first hit taken by the mage.
Boots of Speed.
Boots of Levitation, which would allow the player to travel a few feet off the ground. This would allow him or her to cross fire unharmed and to pass over traps without triggering them. They might also allow player to cross narrow streams/rivers without a bridge.