In reply to jibberingwreck: Depends on the length of routes - when packing for destinations unknown I assume a max of 2 bolts every 5m, so for a crag with routes up to 30m long i'd plan on carrying twelve draws for the route, plus two for the lower-off. Plus an extra if I drop one. I usually take mostly short (10/12cm) draws with two 20cm ones, and if it looks like the route meanders a bit or the bolts are oddly placed then maybe replace some of the short draws with 30cm draws. Might even take a 60cm sling tripled-up to make a 20cm draw that will extend for badly-placed bolts that create rope drag (also useful at belays and equalising lower-offs!)
In summary, about 14 short 'uns and 3 or 4 20/30cm ones plus a 60cm tripled up should see you though anything
Don't forget to pack your cow's tail too!