Since you can't really use a Hi-lift on your Sammi (yet), MAKE SURE that your jack can actually do the job BEFORE you need it. I carry a 10 Ton bottle jack that can raise my Bronco up enough to change out the 35"s it is on, and a piece of 3/4" thick by 12"sq plywood for a base to set the jack on, since mud absolutely sucks when trying to use the jack. don't forget the handle for the jack (
) and maybe a few extra lugnuts. A tarp for groundcover is also nice, and can be used for other needs, such as a tent, to wrap up things, etc...
As for the tire pressure, everybody will most likely have a different idea, so I would start at around 12-15psi, and go from there as YOU feel comfortable. Don't forget some thing to air the tires back up with.