I would suggest a spell to create olive oil that lasts for a month. It can be enchanted into an item, or simply cast once in a while to resplenish supplies.
It's a simple spell, CrAq (He) 10, so depending on his Arts he may be able to invent it in a single season.
The lighting will not be magical in itself, but free fuel is free fuel... 
EDIT: Or he may simply invest the efect directly into a barrel, as a barrel gives him a hefty +5 Form & Material bonus, making it easier to create the item than invent the spell.