Try this: get a timer and set it for 15 minutes. Pack for those 15 minutes. When the timer goes off, take a break, for about as much time as a cup of tea would take (if you break by doing something that would suck you in, like the computer, then use the timer to remind you to stop your break). Then pack for another 15 minutes, then break. Do four of these 15 minute pack sessions, and then take a longer break (for lunch, a walk to the part, whatever). When you come back, do another four. Then assess your progress. Focus on how much you have gotten done, not how much remains. Pace yourself based on how much time you have remaining.
This is my mantra to get things done that seem overwhelming or that I don't want to do: I can do anything for 15 minutes and it won't kill me.