First make sure everything is in good running/operating shape. You want to minimalize the chances for any last minute or unexpected surprises.
Second, for Baja, So Cal, and many other places 31" tires will work just fine. Just make sure they are good tires, like the BFG a/t's, and carry a good spare along with tire plugs. If you find yourself needed bigger tires, then upgrade. Also make sure your suspension can handle the added weight of all the gear you will be carrying.
Storage is a big issue, especially with a 40. Find good boxes or crates that hold stuff securely and can be strapped down. The auxillary outlets are a good idea, along with the second/dual battery. This works really well, and is almost a necessity if you have a fridge (a word about that, fridges rock! once you've experienced one it will be difficult to imagine life without).
Then travel...You will figure out what you need and what you don't. Spend less money on "extra" mods and more on trips!
