One of my summer jobs in college was as a packer, so here are some tips:
They probably will not pack aerosol cans or liquor, so make sure you take those.
Most won't take plants, or if they do they don't guarentee that the plants will make it if it is a long move.
If you have a junk drawer, you might want to clean it out. If we had to pack a junk drawer we would dump it on our packing paper, roll it up and pack it.
If they are packing you one day and moving everything the next, make sure they leave a couple of boxes open for your bedding and possibly a few dishes if you are eating at home. Which leads right into the next tip:
Make sure your dishes are clean. We went into one house and the lady had a dishwasher full of dishes that were dirty. We told her we would pack everything else while the dishwasher ran and then we would pack those. She insisted that we could just pack them dirty. Well, we couldn't do that because it would attract bugs, rodents, etc to the truck. She got very upset that she had to actually have clean dishes!
I would NOT let them pack my photo albums or scrapbooks. Maybe I am paranoid, but these things to me are not replaceable so I would want to keep them with me.
Make sure your frige and freezer are cleaned out -- give it to the neighbors if you have to.
If it is a total pack, they will pack everything unless you tell them otherwise -- this includes most food, your coffee pot, etc. If there is anything you need for the rest of the time you will be in the house, make sure you pull it before they start packing.
Also, one last tip remember these people will be going through drawers, cabinets, closets, etc. If there is anything you would be embarrassed for them to find -- they will probably find it!! You wouldn't believe some of the things we found!
Good luck on the move and the new home!!