I started like Michael suggest with 3 cases, they fit my rack and then some.....I also took a tip from Corrie and we make a list of what we wish we brought, what we should have brought (Diff being one you should have the firs you would like to have) and a list of what we did not need to bring. We do the list on every trip, we now have it down with a longer trip dispersed camping (say a week) and a couple days.....
A recent great video Michael did about what to pack turned me onto a quick grab boox, you wills ee in the vid here:
Here are a couple links to OB lists/gear:
Overland Trip Packing - How to Guide to Get You On the Trail! The Ultimate Overland Checklist - Overland Bound Overland Trip Planning: Know Before You Go - Overland Bound
DO NOT go out and drop a ton of money on stuff, you may find you bought stuff you really dont need or like, I spent a lot of time on here asking about things, good example is a coffee press, never heard of such a thing, but when I asked what people did for coffee, that was one I grabbed onto, I love it! Best thing I bought! Anyway you get the idea.... Ask learn.
Forget your vehicle mods till you are 100% sure of what type driving you will be doing , will you be on forest roads or will you need to crawl over boulders to get back into a sweet spot? Maybe a bit extreme but you get it.... Also like camping gear, go slow and DO NOT spend a ton till you do research.
Last DO NOT wait to have everything perfect (gear or truck), get out there, go spend an overnighter someplace, enjoy our beautiful country... Just get out and do it.
Jim
PS think about communication both regular and emergency, out them on your list!