The bag you reference is way too small and way too expensive. You can walk into any REI or similar decent outdoor store and get a backpack that will be more suitable, cheaper, and more comfortable. I would suggest a bag with about 4,00 cubic inches (65 liters, more or less) with adjustable, comfortable suspension.

My basis for this statement is three decades of SAR experience, during which I learned to keep a pack ready to go with critical items already loaded for instant deployment. I also used a backpack doing field work in archaeology and many climbing/hiking trips for pleasure.

Situations and environments vary, so what specifically worked or me in southern Arizona may not be what you will need. This is something that only experience can teach and much depends on individual preferences and local conditions.

Even today, my hiking day pack is typically stocked with the basic essentials. I also have a CERT pack also ready to go, stocked with items more likely to be used in an urban environment.

Getting a suitable pack is not easy. If possible, rent a model first or possible borrow one. In the store, walk around with an appropriate load as you make your choice. Be sure the vendor has an acceptable return policy.

Modules are a great idea. The various containers should ideally be differentiated by both color and feel. All too often, you will be groping blindly in the dark, trying to grasp the right container.

I focus on backpacks because you can easily be reduced to foot travel, taking only what you can carry. Any available vehicle should be fully stocked with more supplies, fuel, rtc.