- having sex
- storing up food provisions and other pleasurable goods and subsequently enjoying them
This is almost like the 5 precepts, although the the drinking of intoxicants seems to be omitted. The five things are possibly not exhaustive, though, as the book's translator notes that DN 29.26/iii 133 that there are four other things that the arahant cannot do: he cannot take a wrong course of action because of desire, hatred, fear, or delusion.
I have heard elsewhere that an arahant is incapable of breaking any of the monastic precepts (of which there are a lot), with the single exception that he might inadvertently eat after mid-day. Take that with a pinch of salt, though.
It is interesting to note that it is commonly held that a stream-entrant cannot break the 5 precepts. It would be good if someone could produce a reference to the canon that backs this up.
In76.52, Ananda tells us that although an arahant has destroyed all the taints, this fact is not continuously and uninterruptedly present to him. "He knows 'My taints are destroyed' only when he reviews this fact".