Optional equipment that may be quite useful are repair kits, river knife, rescue gear, tube tent for shelter, or a space blanket bivy sack.  I would weigh the benefits against the extra weight though.  Heavy boats can be more challenging to paddle and certainly are a pain carrying.  A cell phone in a Pelican box is a really bright idea though as it doesn't weigh much and may help save someones life.

Outfitting your boat and helmet are generally essential in this sport.  A loose fitting helmet often exposes the forehead to impact and concussions.  A loose boat is much more difficult to control.  Here are some useful articles on outfitting:

• Outfitting Boats
• Outfitting Helmets

A spray skirt is used to keep water out of your boat.  These used to be made in nylon or neoprene.  Neoprene is the only way to go for whitewater.  The first order of business is to get one that fits your cockpit.  Make certain the skirt is well constructed as it needs to stretch significantly to make a tight fit.  Beware of skirts that are really difficult to stretch since we sometimes need to attach our skirts in less than stable areas on the river.  The front grab loop must also be sturdy making it very easy to rip off so you can quickly escape your kayak.  An even better system is a strap that crosses over the middle of the skirt.  A common safety hazard is accidentally tucking the front grab loop under the skirt - always look before you launch.  The tunnel is worn around your waist and needs to be quite snug to prevent water from seeping in.

There are a number of custom and mass produced skirt companies to choose from:

• Skirtworks Note: Excellent quality and customer service.  They also make custom skirts.
• Immersion Research Note: Decent products and excellent custiomer service.
• NRS: Note: Great mail order company with reasonable prices.

Prices range $75 - $180 for new skirts.  You can pick up use skirts for considerably less but may need to make repairs. AquaSeal makes decent products for repairing neoprene although I always prefer neprene cement (not stiff and is strong as new).  Avoid the Harmony brand of spray skirts which perpetually leak and are impossible to seal.  Also avoid nylon spray skirts as well.

Kayak trim is all about having the boat rest in a neutral balanced position in flat water.  If the stern is heavy, smaller holes and ledges will be more grabby and often cause back enders when you least expect it.  If the bow is too heavy, you will be pushing water all the time or need to lean back a bit to lift the bow placing you in a more unstable boating position.  Side to side balance is also important.  Although you can guess whether you are bow or stern heavy, it is far easier to have someone else observe your trim when you are in the water.  Most kayaks start with their seats in a reasonably balanced position.  We then add gear like heavy throw ropes, pin kits, first-aid & repair, lunch, water, etc.  Since behind the seat is easier to reach, we typically stuff all that gear in the back of the boat.  At least try to balance the load spreading the weight evenly on each side.  If the stern of the boat is sinking, one approach is to move the seat up one notch at a time (the foot bulkhead will also need to be moved up as well).  Another neat approach is placing seldom used gear in a float bag in front of the foot bulkhead - perhaps the first-aid and repair kit is a good choice.  Consider spreading the load of group gear, one person carries the 70' heavy duty line, another carries the big first-aid kit, etc.  Many boats have ways to carry water bottles in front of the seat and water does weigh a fair amount.  Your goal is to be able to sit upright in flat water with a reasonably balanced boat.