Don't think too far into it. I have a military style bug out bag that would last me a week or more. however...

In my car I took a regular (yet not cheaply made) school backpack and filled it with water purification tablets, a small filter, two bottles of water + a container, misc food to last me 3 days (no MRE's, just nonperishable stuff), matches, lighters, dryer lint to start fires easy, compass, ADC road map of the area, spare underwear, 3 pairs of socks, pants, shirt, jacket, poncho, a tarp I keep in my car, a good pocket knife for a tool, a boot knife for a weapon, flashlight, AA batteries, 40 rounds of ammo for weapon, cheap rifle I LEGALLY keep in my car. I also have a portable HAM radio with a good portable slimjim antenna, this is optional but TO ME its the most important part because thats how I contact with my group.

Now is it fancy? No. Will it let me survive for 3 days? You already know the answer.

Before you worry about fancy equip make sure you can do what I did and have what you need in a BOB.