lol that's a good idea, we still use a 12 inch carpenters level we keep in the drawer.

+1 to Harbor Freight black rubber wheel chocks. And we use lego blocks for leveling and the little triangular screw things for stabilizing (they came with my my 1961 trailer). We also use these jack pads under the jack foot - protects the grass if we are on it, we dont have to extend the hitch foot as far, and it can go under the jacks on soft ground: https://www.amazon.com/Stabilizer-Jack-Standard-x6-2-Yellow/dp/B000BUU5XQ/?th=1