I thought chain breaks were pretty rare so was a bit surprised it happened, although after the punishment of the cold my trike has suffered recently I suppose I shouldn't be so surprised.
I have the 9spd powerlink and chain tool at home. I don't think that I'll take to carrying them around on a daily basis, however, as it adds weight to the tools. I'm off on a cycle tour on my own in Germany in May and need to think very carefully, before then, as to what I should take and what I can reasonably safely leave behind.