I too echo the sentiments of Gibbon and Smoketrails.
And like the OP and OFSO I always tap the outside of the plane before walking through the doorway. I used to think it was just a weird habit I had, but am interested to read other folks do the same.
Once seated I always check there's a life-jacket under my seat too. Fortunately I've never had call to actually need to use it, but on one occasion I did find that the life-jacket was missing. Makes me wonder what kind of moron would steal a life-jakcet?!