If you let the Ring of Sustenance get your spells back in 3 hours instead of 9, it could be worth it. Rations are cheap, and starvation (aside from Fatigue) isn't so bad in D&D. You can even stretch them if you don't mind RPing intense hunger pain (or were raised in a monastery so you don't care), since you only risk nonlethal damage/Fatigue after 3 days without food. Fatigue isn't even so bad for a Wizard.

It depends on what you're getting out of those extra six hours, especially if the rest of the party still has to sleep the full 8.

Don't forget buying spells known. Especially if you take the oh-so-broken Uncanny Forethought.

Seconding tons of low-level scrolls (Scholar's Touch can be great if you're a busy adventurer doesn't have time for book-learnin'), or single-charge wands if they're available. I imagine scrolls would be like mundane items, so you'll want to occasionally glance through your list of scrolls while dealing with problems so you don't run into a "forgot my powers" situation.