It depends on your ability to make a diagnosis and fix the car at the side of he road, I normaly take enough tools and spare parts to carry out a minor rebuild,
Gaffa tape, rad weld, rtv silicone sealer, insulating tape, random bits of wire, various eletrical terminals, cable ties, nuts bolts and washers, jubliee clips, fuses, various bulbs, brake fluid, brake cleaner, WD40, rope, coil, 4 plugs, condenser, HT leads, half shaft (only in the Dellow), fan belt, water, ptfe tape, engine oil, axle oil, hand wipes, latex gloves, ground sheet, grease gun, jack, foot pump, wheel brace, copperslip, exhaust U bolt, octain booster/lead substitute and some clean rags, and tools.
If you don't fancy that then I would go for the mobile phone and RAC card option
