Are you flying from the United States to the UK or somewhere else? When I fly I wear a "safari" style vest and in the pockets I keep:
1. compass
2. whistle
3. AMK Heatsheet
4. gum
5. 20' of paracord
6. small first aid kit (bandaids, asiprin, imodium, antihistamine, antibacterial wipe)
7. book
8. tiny MP3/FM radio thingy
9. ear plugs
10. small pack of handiwipes
11. toilet seat covers
12. Signal mirror
13. Fresnel lens
14. two bottles of water (purchased after going through security)
15. High-energy snacks
16. dog tags (around neck)
17. fingernail clippers
18. pen
19. pencil
20. small pad of paper
21. deck of cards
22. small, single AA LED flashlight

Most of this stuff is comfort items in case I get stranded in an airport. My understanding is lighters are allowed back on board but haven't tested that yet.

-Bllast