I have had it when only the legaly required minimum was sent. This was from companies that have been sued for a bad recommendation in the past.
Others would make a copy of everything in the personal folder. PRIA records from employers in the past, my written requests for base and route assignments, promissary note to stay x amount of time, resignation letter and exit interview smarta$$ answers were all in there.
What they are exactly asking for will be listed on the request form that you will be signing, one for each employer in your history for 5 or 10 years. Most of the time they seem to take the list straight off the resume or employment app if there is one. Make copies of what you sign. Check the box to request copies sent to your address.
Requested are training records, checkride forms, drug test reports and most likely some sort of circle Yes/No "Failed drug test", "Eligible for re-hire" etc. questionaire.