BOLTS - B*ggered if I can remember

[Grahamm]

That's been extended further now:

P - Petrol
O - Oil
W - Water
D - Damage/ Drive (chain)
E - Electrics (lights)
R - Rubber (tyres)/ Reflectors (mirrors)
S - Suspension/ Stopping (Brakes)

I've also seen another version: POWDERY where the Y is "You" ie that you're wearing all the right gear.