Who else's got a wet trunk?

For drying it out, nothing special - clean out as much as you can with towels/vac/etc, and then get as much air circulating as you can.

For the leak itself, if it's the sunroof, the water is more likely to come from the sunroof itself and you'd see it raining on you along with wet seats. I'd wager it's more likely the trunk itself or a light assembly that's leaking.

Simplest thing to check is the trunk seal. Open the trunk and check around the seal for tears or areas where the seal is no longer attached. If there is any debris built up, clear that out too. Pour water around the outside of that seal and see if anything is coming through. Some weatherstrip adhesive fix up any cracks or breaks in the seal.

The other place you could be getting water in is the lights. Check around the housings to see if their seals are still intact and you can test by pouring water to see if any moisture is coming through. The "correct" fix here is to have the light housing removed and the gasket replaced. That can get spendy if you're not doing it yourself, though, so some clear silicon can be employed to seal up the gaps.

Now, I doubt it's the sunroof leaking, but just to be thorough: The sunroof has drains that can get clogged over time (usually see it with older cars or those that park outside under trees). Open the sunroof and check around the opening for debris. You should also be able to find the drain holes. They're small and run through the frame and out the bottom of the car. You can test to see if it's clogged by pouring a small amount of water into the gap and seeing if it drains or not. Some compressed air into the drain holes is usually enough to blow any loose debris out the bottom and clear the clog if there is one.