Wear your No 5s - if they fit!
Seriously, there is nothing worse than seeing, say, a slightly portly FltLt bulging out ofi a very tight Mess Kit that was 'tailored' when said chap was a whippet of an APO. These guys look like Northern pub singers!
If you have tropical Mess Kit (No 8) - its a lot more comfortable than No 5s and rather smart, too. However, expect to be asked for ice creams! Deffo wear your medals. Consider it part of a pubic IO campaign.