One critical item in any kit is rain protection. Wet clothes can lead to hypothermia which could lead to death. Every type of emergency kit (home, vehicle, hiking, and B.O.B.) should include rain gear. Rain gear can be as simple as a $4 plastic poncho or as elaborate as a $200 GoreTex rain suit. Buy the best rain gear that your budget allows and remember that you can always enhance your rain gear later.
Wet clothes are heavy and rob your body of vital warmth. Rain gear helps protect you from water so that you can better maintain your core temperature. Wet clothes can cause a drop in your core temperature which could lead to hypothermia. A trash bag or plastic sheeting could provide some protection if you find yourself without proper rain gear. Be sure to have an extra plastic poncho or two. Plastic ponchos are small, inexpensive, lightweight, effective and you can use them for backup or you can give them to others who are not prepared.
GoodYou can find simple, plastic, emergency ponchos in a wide variety of retail outlets. These ponchos range in price from a dollar or two to about $15. I highly recommend having a few in your vehicle kit and at least one in your hiking kit. These are small and inexpensive and you may want to have extras to give those who are unprepared. Keep these ponchos as extras even if you upgrade to better rain gear.
BetterIf you want better and more durable rain gear then consider a heavier plastic rain suit or something like a Frogg Togg suit. These suites include jacket and pants and are very effective at protecting you from water. I wore some Frogg Toggs on a rafting trip and they kept me very dry. There are a variety of rain suits and they range in price from about $15 and up. Expect to spend $20-30 for a decent rain suit. These suits will be more durable and can be used over and over. These suits will be heavier and more bulky than the simple plastic ponchos and may not be the best choice for hiking kits where space is limited.
For maximum rain protection and minimal size consider a lightweight, waterproof, packable, and breathable rain suit made from GoreTex, 4Most DryPlus (Cabela’s), or similar fabric. Expect to spend at least $100 for a high-quality rain suit. The retail price for my suit (jacket and pants) was about $160. These suits feel like a windbreaker and compresses to a very small size. Make sure the suit is large enough to fit over bulky layers.
I choose Cabela’s Space Rain jacket and pants because these are 100% waterproof, very packable, lightweight, reasonable durable, and very effective. A set will be a fairly sizable investment (pants about $70 and jacket about $90). These garments are meant to be used for years and come with a lifetime guarantee against defects. These come in a variety of camouflage patterns and sizes.