Blocks for the leveling jacks are usually not needed on packed ground, gravel, pavement, etc. You may need one on soft ground, and you may need one under the tongue jack if the open-pipe end of the stem sinks into the pavement. I carry a few pieces of 2x6 or 2x8 board, each 10-12 inches long. These are great for leveling, and for the tongue jack. And they are also very useful if you have to jack up the trailer to replace a tire, where curved levelers don't work. And if one gets lost or broken, it is no big loss.