Depending on the weather; you might want to budget more or less time.

Hike the trail. Take the long way. It will be a dawn til' dusk day but totally worth it.

Walk through all five towns, my favourite Riomaggiore.

I've been to Cinque Terre Twice.

First time pissed rain sucked left in 48hrs

Second time weather was pristine and realized how important nice weather for Cinque Terre is.

Food is expensive, not much in the way of groceries stores, stock up before you get there.

Nap on the beach, the further down the coast you go the more rocky it becomes.

Cops will find and kick you out if you try to camp out on the beach over night. In a tourist area like this, cops are everywhere.

Not a huge party scene, however, Riomaggiore has a rock beach on the far south side. Start a fire and all the backpackers will show up.