Today a video was posted on the Halloween event, showing some of the stuff:
Video: Guild Wars 2 Halloween update video: Chris and Tom try on costumes, throw things at kids | Videos | PC Gamer
Go to 2:13
You can clearly see the recipe "Strawberry ghost"
Which would indicate Strawberries will be used to make this, thus making them a highly demanded item.
Invest now,r eap the rewards later.