Pick up any catalogue from a tool supplier and the range of tools available is vast. However 95% of these you’ll probably never need, or may need once during your ownership of the car (so hiring or borrowing from a mate may be the best bet there!). Stuff I wouldn’t leave home without must include the following: A range of screwdrivers, both flat and cross headed in a variety of sizes (but a reasonable quality set too, the cheapo ones just snap when you lean on them), a set of spanners suitable for your particular car (i.e. don’t go buying a metric set if you have gone and bought a 1950s Sunbeam).
A tin of oil and bottle of water/antifreeze is always a good thing to have kicking around in the far reaches of your boot in case of emergency, as is a towrope and quality set of jump leads (not the £1.99 set from Tesco’s either). Other less obvious things to include may be insulation tape, rubber straps and some string to tie things back on with! .