Associated with tax refunds are return journeys.
One that is clear cut it a journey to an airport. If your spouse drives you there you can claim her journey home and then the one picking you up. It was in QRs I believe but I am out of touch now. Naturally these then attract tax relief on the different rates.
I was also able to claim for journeys to rail stations. As far as MOD is concerned you could claim back 3 years on unit and a further 3 years on application through the central records.
Then on tax remember you can also claim subsistence difference too, not just on hotac and overnight but lunch/dinner too. What used to get me was the duty journey, say 10-14.30 buy lunch but no claim.