Looking at mine, the main things I have (and use occasionally) are:
- Chart of UK LARS areas and frequencies
- Main transponder codes (N.B. Not always the same here as in the USA!)
- Quadrantial rule
And don't (often?) use, but would probably not choose to delete:
- SAR ground signals
- Flight plan sequence
Also rarely removed from any of my kneeboards is a standardised light aircraft checklist which I've simplified and reduced to A5.
G