I carry about 10 pieces of these. 2 x 8 x about 1 foot long. They happen to be pressure treated, but I don't think that matters. I use them as shown for leveling, and also put them under stabilizer jacks and landing gear when needed.
I've never understood why people would carry long pieces. There is no benefit to having a single piece of lumber stretch between tires. Take that same long piece of lumber and cut it into 12" or 16" pieces and they are much more useful and easier to handle.