I'm sure I answered it before, but my nav-bag is sat here, so let's see...
GPS
Spare strap
Calculator
Control force gauge & tape measure (I live an interesting life)
Kneeboard
gash trip logbook
type data cards
RAF Flight Information Handbook
RAF Minor airfields guide
Pooleys
Torch
Pens and pencils
Spare batteries
Stick-on compass roses
Flying Gloves
Baseball cap
Loo roll
Assorted charts
Dalton computer
Blank ASI Calibration charts
Scale map rule
(where the hell has my protractor gone, it should be in here)
Couple of old flying magazines.
Swiss army knife.
There's usually a cockpit voice recorder as well.
G