Don't forget food/treats/toys for the four legged one and put together a first aid kit for yourself and for the pooch. Bring multiple leashes and collars. Plastic bags to clean up.

Check the laws in the states you are driving through as pertains to your Glock. It won't do you a lot of good locked up in a box in the back and it might land you in jail if "concealed".

Check the weather along your route every day to avoid a nasty surprise - you might want to re-route rather than getting stuck.

Consider carefully what kind of "offroading" you'll be doing. Will you really need AT tires? If you're heading into snow, then you'll be far better off with actual snow tires - AT tires aren't that good in snow - especially on road.

Have you really been an area where you needed a gas can? It seems like the majority of travel will be on real roads and if you expect to be driving late into the night then just gas up early and often.