@Brent S
Since when have normal folks made good decisions? Now add in dehydration and limited diet and they are done for but not as fast we we think. I just finished watching a Documentary on the sinking of the USS Indianapolis (per accounts from the actually survivors). Those men spent 5 days in the water and most were still able to make good decisions at the end. The weak of mind and spirit (non-believers) will perish first, by the end of the third or fourth day. The tough old birds will last until the 6th. or 7th. day after the water runs out.
To me, a nation wide pandemic SHTF will be the most dangerous event. It will be a very slow break down in services and be very difficult to manage your own supplies, due to the unknown length of the event. This type of event provides the most time to get out of Dodge but will also make the highways dangerous too. The government is going to want to limit the potential spread, so contaminated area's (cities) could and probably would be quarantined. Outlying towns will help enforce the quarantine. They are not going to welcome a boat load of possibly infected city folks.
A grid down situation will be the easiest for a prepper to survive. It is going to be very fast acting. The gangs will not have enough time to band together and plan any viable operations. It is going to be every thug for him / her self. The lack of water is going to be the limiting factor. It stops flowing as soon as the pumps shut down. Thugs have massive street smarts but engineering is not their strong suit. By the time they figure out (just like the majority of folks) that the power is not coming back on, they will already have one foot in the grave yard. I think the main die off will be over within 2 months. Knowledge of water purification and distillation will be critical.