Since everyone here is talking about party comp, I might as well be transparent about my own plans. 

I'm designing two characters, specifically with the intention of being able to fill the roles that the party needs if necessary. 

The one I'm currently working on is a Tiefling Witch who will act as either the primary debuffer/battlefield controller or a party support using the Healing Hex, some Cure spells and all of the buffs. As a debuffer, I'll be running a Winter Witch (which is absolutely my preference). As a support, I'll likely run Hedge/Herb Witch combination.

If we're looking for someone in melee, I could run a mutagen-snorting Alchemist. Most likely a Beastmorph/Vivisectionist. The build would mostly focus on damage and utility, but should be able to soak as well, if needed. 

Regardless of setup, I'm probably doubling as face or off-face with some well-placed traits that swap CHA for INT on some social skills.