What's in my Envoy now stays in there all year long. The only things I add for winter are an ice scraper and one of those cheap collapsible shovels to make quick work of powdered snow. Otherwise, going from memory, this is what's in there:

In the front (center console, glovebox, door boxes):
-Prescription sunglasses
-Streamlite Scorpion
-Maglight 3D cell LED flashlight
-Microfiber towels
-A container filled with spare change
-A gerber multitool
-A benchmade seatbelt cutter
-A handheld CB
-Work Gloves
-A pad and pen
-My Garmin GPS
-Cell phone charger
-Box of tissues
-Various snack bars

Under the back seat:
-Crow bar
-Small Utility Shovel
-Gerber Hatchet
-Plastic Funnel
-Tire changing tools (wrenches and jack)

In the rear:
-My toolbox (filled with all kinds of hand tools and other little bits and pieces like spare bulbs, fuses, tire plugging kit ect ,ect)
-A quart of motor oil
-A cloth cooler bag filled with water-bottles
-A stainless Nalgene bottle
-A fleece sleeping bag
-A bright yellow windbreaker jacket
-A sweatshirt
-An umbrella
-A couple flares
-Jumper cables
-A small first aid kit
-A fire extinguisher
-Gloves
-Tow straps
-D-Ring Shackles
-Power inverter
-An extension cord
-Disposable Shop towels
-Bungie cords
-More Snack bars
-Towing reciever ballmount
-100ft of climbers utility cord
-Big garbage bags
-A little zipper bag with:
--N95 dust mask
--candle lantern
--Prescription goggles
--A Doug Ritter PSP
--Water purification tablets
--Disposable Poncho
--Small roll toilet paper
--A lockback pocket knife

The vehicle has a built in air compressor in the back right compartment, to which I just added an accurate tire gauge and some different nozzles.

If I'm going somewhere where I don't expect to see a lot of other people, I'll toss in a 5 ton come-along and maybe a filled 5 gallon gas container or two....but that's only when I feel like I might need 'em.