I use the Outdoors for Life jack pads. They have a nice case to store them in and come with handles that make it easy to put them in place and put them away. I have been using them for almost 5 years and they are still in great condition and have worked well for us.
For soft ground I made my own out of several layers of green 3/4" pressuretreated plywood glued together with Gorilla glue. They're 16" x 16". Have used them for five years and they're still fine.
Either nothing or, if the site is very unlevel front-to-back, some of the orange "Legos" from Walmart. The large steel plates used at the bottom of the landing gear are made to interface with the ground.