In reply to iamaclimber:
I double up all of the smaller sizes that aren't matched by an offset; i.e. 1, 2, 3.
I have found that I have used both doubles on routes in north wales, but I have never come across a situation where I wanted three of a rough size (which you would have if you doubled up nuts 4 onwards - e.g. 4, 4, offset 7 all are the same rough size).
However I do carry HB's and RP's (mainly for the slate).
Post edited at 15:14