A good idea of the wind and how it's likely to change with altitude is good. If you're in a hold and have access to a surface wind, it's good to be able to estimate the wind at your level. Having said that you have an FMS to do that for you
A good understanding of icing conditions, when icing is likely to occur and how severe it might be will be good, but nothing like seeing it for real for the first time however many books you've read.