Another posibility I thought would be the long term stamina be used to restore the short term stamina.
Short term stamina is used on everything, from walking to attacking or casting spells. By resting the short term stamina regenerates faster.
Long term stamina is used to regenerate the short term stamina, being regenerated only partially by eating, or completely by sleeping. This would have enough capacity to last at least one or two days but the lower it gets, the slower the short term stamina is regenerated.
The same occurs when casting spells, it drains mana, but also a little cuanty of short term stamina, the less mana you have the more short term stamina it requires.
Food would be used to regenerate a percent of long term stamina (but you wouldn\'t be able to replace sleeping with eating) and to regenerate health. If you exhaust your food points, you will stop regenerating health and long term stamina but you wouldn\'t die which would be annoying and not usefull to a game.
edit: typo
