I learned several important lessons during Katrina. During the two hurricanes prior in the area (Danny, and then Ivan the previous season), I was the guy who got made fun of for being "over prepared". We were told to report for duty with 3 days of supplies for ourselves and anyone sheltering with us. I brought enough for 6 days. Amazing how their attitudes changed during and after Katrina.
Three important things to consider for your bag:
1) How many days do you intend for the supplies to last the four of you?
2) How much material can you realistically move at once with the available manpower and machinery? What happens if a person or vehicle in your plan becomes unavailable to carry supplies?
3) Are there any special considerations that will impact both your supplies and logistics? (Age, health, disability, etc.)
Finally, when considering your weapon, you have to know what applications you'll be using it. This includes the physical environment, and the situational context:
1) How much range do you realistically need?
2) Who/what is the likely threat to be encountered?
3) What are the state and local regulations on how you can carry or transport your weapon and ammo? What happens to those regulations if martial law is declared? (See what the police and LA National Guard did in New Orleans area...)
4) How much ammo can you realistically move at once with the available manpower and machinery? Also, in a tactical situation?
I was rolling around off base with my privately-owned weapon, 30 rnd. mag + 1 in the chamber, and an additional 3 30 rnd. mags. But the reason why the MS National Guard didn't stop me was because I was active duty at the time, had the ID to prove it, and was running critical civilian supplies from out of the area to a local shelter/de facto supply depot by POV which automatically made me a potential target for looters. I feel very certain that without those credentials I would have been turned back or potentially arrested for openly carrying an assault weapon like that. However, I also feel certain that the MS National Guard was the reason why mass chaos didn't ensue there like in New Orleans - they were on the ground before the storm was even gone. Their strong work and dilligence was why I never had to actually use my weapon there, thank God.