When I am out I carry a section of 2x6 with me to put under the jack if I
ever have to use it in a rough or soft soil situation. If it is a situation
like working on something in the back yard I will use a total of three of
them.  One for under a jack and then two (side by side) under the jack stand
that I will put in before doing any work under it or that will be shaking
it.

For working on something like a wheel bearing I like to put a 4x4 section of
plywood or similar down as my base under the job.  Even when working on the
driveway.  It gives a cleaner surface to set stuff on without getting sand
into the works.

Jimt