i'd put a small firearm in the center console, it should be legal if you keep the mag in a separate place from the gun like the glovebox. if you have your cwp just check the reciprocity laws in the states you travel through and you may be able to carry it with the mag in it right in reach.

 

A stereo with bluetooth and an ipod connection I have a steering wheel remote in my astro van that I drive for work it makes it really comfortable
Water for the dog
Snacks
If you haven't yet fab up some cup holders
Full size spare tire and a 12 volt compressor
Flashlights and batteries
Jumper cables/booster box
Pillows/blankets
Small cooler
Knife of some sort
Lots of fast food napkins (many uses)
Can't think of anything else