You should browse PPRuNe to see the staff travel benefits - one/two free firms per year,plus ID90s, and 20 hotline bookings.

No onload occurs out of priority (in my experience) - it upsets too many people and groundcrew do not permit it - and indeed little shuffling around cabins unless with crew consent - again, it upsets too many people, and diminishes the experience of those paying for the cabin to get unruly children in the wrong cabin. Only out-of-priority onloads occur to keep family groups together, or get staff to base to work if holiday plans have gone awry.

Though the captain can do what he wants (and cabin crew think they can) - diplomacy rules otherwise!