Large Ziploc bags (2 Gallon size are available in the US, I haven't found anything quite as large here) for damp items, and AIRSICK BAGS are awesome for smaller, icky things! (I am so sensitive to soap that I pack my own).
I have a couple sizes of Ziplocs in every suitcase I own ~ they have saved the day on a couple occasions (they make a great makeshift ice bucket or cooler) and I take the airsick bag with me when I deplane ~ they usually end up as a bookmark on my flight
