A decent 20/50 oil for the engine and gearbox, Halfords classic 20/50 is good but I use Comma oil from my local motor factors - it's just as good and half the price
For security I use a Disclock, it clamps around the steering wheel and is a very good visual deterrent as well as being extremely difficult to remove without a key, if you do decide to get one then the large size is needed to fit the standard Minor steering. Also a secret switch to isolate the ignition will often baffle a potential thief
