Well, I'm paranoid that important things will be left behind if I don't supervise and pack the majority of things myself. This stems from my first marriage, when, halfway to Gatwick I realised I didn't know where my passport was. It seems my then husband had taken his passport from the fire-safe and left mine there thinking I would get it myself. I had enough to worry about having done a full day at work the day before, looking after 21 month DS and making sure I had all his stuff (his first hol abroard) MIL staying overnight as coming too, etc.
We had to turn back and drive home to get the passport, DS was included on it in those days. We got to the airport just as check-in was about to close, meaning sitting in various seats dotted around the plane. The selfish b-d never even apologised, although he didn't get into a temper. How hard would it have been for him to pick up both passports, and at least give me mine? But that was him to a tee. That marriage eventually ended in divorce.
These days with new DH, he selects what he wants to take and leaves it in a pile on the spare bed, and I pack it into the cases, otherwise we wouldn't be able to shut them. Before we leave the house, I show him that I have the passports, driving licences, tickets, carpark confirmation, insurance and health documents, spare house and car key, as these are the things he worries most about. Once we get to check-in, he takes care of his own passport and boarding card. But he always packs his own stuff for work overnight trips.