Along with my ILBE pack and Ribz front pack that make my INCH system I also have two extra's packs, and a rubbermaid tote. As mentioned this is for BOV use, as the INCH system is my main gear and generally self sustaining but if you can a bit of extra gear is always nice to have. If needed you can cache it if you have to ditch your vehicle, pass it off to others, trade it, or you never know, you might end up loosing your main gear and need it yourself.
My two extra's packs are mainly specific themed but each has a bit of minimal gear to make them able to survivable packs by themselves incase they become primary packs.
The first one is a messenger/backpack type bag with stowable shoulder straps. In it I have a bunch of rations, mainstay bars and survival tabs and water pouches, also some general long term storable food. Included also is head lamp knife, ferro rod, lighter, altiod kit, emergency blanket, etc. Enough stuff to allow me to survive if needed, but mainly geared toward extra food rations.
Second pack is a med duffle bag with extra sleeping gear. Wool blanket, two light weight sleeping bags, heavy (not silnylon) camo tarp. Again along with this gear is knife, fire devices, food etc to allow this bag to make a survivable pack if I was limited to just this.
My rubbermaid tote has longer term gear. My main seed stock for planting food and some basic gardening tools. Luxury kitchen gear, all those great things you would love to have to cook with and on but don't have space weight to bring in a BOB or INCH. The very heavy and space filling tools, they are so important but the weight and space they take often cuts them from the main pack. In this tote I collected as much as was reasonable.
If time and space allow, I would also bring my cylinder stove, and solar panel with portable battery and inverter. Also whatever food I might have in my kitchen that could be brought. This of course depends on how fast I have to go, and who might be going with me and with what gear they might have.
Generally my INCH system is first choice, then I have plans for all these extras as time and space allow. Having the INCH already packed, along with extras prepacked give me a large time advantage over the average not prepped person, adding in bigger and unpacked items puts me closer to the average person's bug out time, but with a lot more gear. Having a sort of plan check list of what to grab though makes it a pretty easy task to load up quickly as possible. If needed I can just grab the Inch gear and be gone in a couple minutes, or take 10-15 minutes and grab all the stuff I can. Speed of bugging out can mean the difference of getting out and getting stuck in traffic though so it all depends on what is causing me to bug out, in general my plans are to bug in but there are reasons that could cause me to bug out.
My favorite quotes from Rorschach from the comic Watchmen
"Once a man has seen society's black underbelly, he can never turn his back on it. Never pretend, like you do, that it doesn't exist."
"None of you seem to understand. I'm not locked in here with you. You're locked in here with *ME*!"