I carry a 10 - 2x6's at 12" long. This way I have enough to use at least one per stabilizer, and have up to 6 for leveling under the wheels. I did chamfer the top sides on the ends to assist in pulling the trailer up on the
tires on the side needing elevating.
My trailer has tandem axles. I have been using this method without incident for many years now. I am not a cheapskate, but when I looked at the price of the plastic stacking blocks, I could not possibly substantiate the cost.