With a family or 4 on just my income I don't have the resources to have a bag that just sits unused, I have to justify my gear by giving it as much use as possible.
My BOB/GHB/whatever you want to call it is a cabelback that I take on bike rides, short hikes, over night trips, etc. As I get the funds I'm starting on bobs for each family member, going to get a camelak for my wife then add a few duplicates of consumables for her to carry too, then as the kids get older do the same for them.
You might br surprised what you can glean from a Salvation Army or Goodwill store for the kids first BOB. Backpacks for $3, stainless steel water bottles for .99, flashlights, raincoats, hats, outerwear and on and on for dirt cheap.