In reply to no_more_scotch_eggs:
A few things, in the order in which they are most used, noting that I have more than 1 bike)
A track pump with a gauge. (every two days)
A decent CO2 inflator for when you're out and about. (every two months-ish)
A chain measuring tool (about £6) so that you can see how worn out your chain is and so can shop prudently in advance before you actually need one. (3 months)
A couple of Power links for your chain and a chain tool. (6 months)
The special nut thing for removing cassettes and a chain whip - don't need those until bits start to wear out though. (6 months- 1 year)
A pair of cable cutters (1 year)
A bottom bracket removal tool. (twice!)