Improvised sleeping gear?

I'm looking to acquire some good camping gear that will help me contend with the frequently rainy conditions around here. I hike light so I pack a hammock and parka/tarp instead of a tent which leaves no room for a sleeping bag. Are there any particular articles of clothing I could pack for camp use that would keep me warm and dry? I was thinking a winter parka and some ski pants might do the trick but that sounds like it may be a little too much. I guess what I'm ultimately aiming for is a "sleeping suit" if you will, to use with my hammock and tarp. Any suggestions?