In the book Of Mice and Men, what do George and Lennie do for a living?

George and Lennie are migrant farm workers.  This means
that they travel from farm to farm, hiring themselves out as temporary labor.  Usually,
migrant workers travel along with the seasons of the crops.  George and Lennie go from
farm to farm looking for work.  In California in the 1930s this was quite common.  It
was a hard life though, because farm workers did not make much and had to do hard work. 
Picking crops is uncomfortable work.  George generally chose the assignments based on
rumor and what they happened to come across.  It was typical for migrant workers to go
looking for work and stop only when they found it, until the work was done when they
would move on to the next one.