I keep a
Camelbak Commander for a bug out bag (BOB). It's easy to toss in the car or use as a pack (which it is). The bladder holds 100oz of water. I keep this one in my bedroom closet (dry) with 3 days of food, changes of socks and shorts, a change of pants and shirt, cash, 1st aid kit, prescription drugs for a week (rotated regularly) and spare ammo. I've been thinking that someday I'd add a folding carbine like a Keltec SA16CA. Not the spiffiest of rifles but it will fit in the pack.
I also keep a
QuakeHold Grab-N-Go kit in my car at all times. If you have kids I'd keep more than one. It's a very-very small kit but I've found enough room in it to add more water, a few extra chem lights, a couple of chemical pocket warmers, a
small flashlight and 2 changes of batteries, and 1 spare cell phone battery. It's so small that you'll never be tempted to take it out of the car. I highly recommend it for the car but it's too small and limited to be a full scale BOB. However it will get you by if caught away from home or if stranded someplace.
EDIT: I also keep a
Blackhawk rifle bandoleer with with my BOB. I like it because it has room for 4x30rd spare AR15 or Mini-14 magazines plus 2 double stack pistol magazines without sticking out like a sore thumb.