That is a sweet skid jack, but I think carrying around a floorjack in your (Non-pickup) vehicle is perhaps a little overkill...
I've had the same "2 Ton" bottle jack that I bought while I was in college for 20 years now. It has been great, lifting everything I've asked it to. I even changed the fluid once! It will jack up one front wheel on my duramax without issue. You def don't need heavier jack than that on a little LR.
Do carry something to put under it in softer terrain, and understand that most jacks are not terribly stable. (IE, they need the parking brake set, wheels chocked, etc. to keep the truck from rolling/tipping off the jack.) I even used my little jack to get unstuck from some muddy ruts once when I accidentally left my hi-lift at home! (Not recommended...)
As for junkyard jacks, you might also look into the screw-type bottle jack that has come in every XJ and TJ since the beginning of time. They are simple, compact, don't leak, and have a really good lifting range! They do NOT like to be dunked in mud, so you'll want to find a relatively clean storage place. And get the handle that goes with it if yours is different. XJ's have a nice handle. TJ's use a bagged erector set-style dealio, which I suppose is fine if your LR has 19mm lug nuts. Not sure what's in a ZJ or WJ, but they're probably the same.
Good luck!
Chris