1. Check your line lengths, all four lines should be equal when your trim is set for maximum power. Tie the ends of your lines to something, unroll the lines from the bar, and check that they are equal in length. Lines can stretch (or shrink) and regularly need adjustment to make them equal. Most bars have knots on the outside lines that can be moved to compensate.
2. Inspect you kites for damage. Check for cuts or scuffs on the leading edge or near it. A small cut in the fabric can grow to a major failure when stressed. Small cuts on the canopy (smaller than one or two centimeters) can usually be patched with self adhesive repair tape available from kite stores (or marine stores as spinnaker repair tape). Any cut on the leading edge is a bigger problem.. North Sails in Richmond does very good kite repairs.
3. Lubricate you pump. Don't use oil as any petroleum product can damage the the seals. Silicon lubricant is a safe bet.. spray cans are available at most hardware stores or bike shops. If you have been kiting at sandy beaches you may also need to open the pump and clean out the sand.
4. Reinforce your pump hose. It is very common for the pump hose to break where it gets kinked near the pump. Just cut the hose off and re-attach the slightly shorter hose. Use a little glue. Then wrap some electrical tape around this hose area to reduce the hose kinking there in the future.
5. Wetsuits need attention. Check for rips and try to glue them. Wetsuit glue is widely available including at dive shops. Wetsuits have a limited life and maybe it's time for a new one. North Shore Ski and Board has a good selection. Most kiters use a 5/4 wetsuit in the colder season. Wear a polypropylene or wool (not cotton!) shirt under your wetsuit on really cold days.
6. Get a hood. Everyone needs a head covering on cold days. The heat loss from your head is very significant.
7. 5mm booties are really nice on cold days. Gloves or mitts really help too. Be sure to get gloves that are pre curved and don't require you to squeeze much when holding onto your bar.. (which will rapidly tire your forearms).
8. Check your harness for wear. The straps holding your spreader bar are usually the first to wear out. Any shoe repair shop can do the heavy stitching that may be needed. If you use a rope slider bar, check the rope for wear.
9. Check your board for cracks or delamination. Often a little epoxy (JB Weld marine epoxy is widely avialable) fixes things. Aso check that your footstrap screws are tight.
10. Check that you have sunscreen and sunglasses in your kit bag. Think of these as safety gear. UV damage is cumulative so protect your skin and your eyes especially in the summer.