The name says it all. Sewing Kit - These are real handy and don't have to be elaborate at all. It has rained on us for 6-7 days straight. Last year was the rainiest season, yet. Gore-Tex seems to work nicely but, it is expensive.
Ponchos also work.
The choice is yours. Remember, if it's raining cats and dogs and we need to get up and pack and move on to the next site, we do it. Spare eyewear - extra contacts, glasses, etc. Warm hat - These really help retain body heat. Jewelry - You must be very careful with what you're bringing.