Here's some from my list:
A PFD for each person, REQUIRED
a whistle on each PFD, REQUIRED
a VHF Marine radio,
water to drink,
a hand sump pump,
a bow line,
spare parts (rudder pins, aka shear bolts, some extra spectra line, wire-ties, etc.),
SS tools to tighten everything and install all spare parts,
If going solo off shore, or in rough conditions, a surfboard leash for each person.
If you are going way off shore, an EPIRB.
Here's a couple of old post of my AI toolkit contents: http://www.hobiecat.com/community/viewtopic.php?t=10418&highlight=
(I really should update for the TI)http://www.hobiecat.com/community/viewtopic.php?t=8424&highlight=
- - - - - Hobie Island Sailing since 2006 - - - - - 2011 & 2015 Hobie AIs and a 2012 TI