Get out and walk around the plane, even if you've just stopped in briefly somewhere to drop something off. Even if you are in a hurry, a 30 second walkaround isnt going to hurt. Theres nothing like taxiing out in a 206, putting the flaps down and realising the back door isnt latched properly and the flaps wont move to remind you of this. Of course if you dont notice until halfway down the runway and it wont fly then it wakes you up even more!!
Then of course then theres fuel caps, oil caps, baggage lockers...the list is endless!!