Possible explanation for the purple bags.
We know from the autopsy report that PB had advanced prostate cancer. As such it is highly probable that he suffered from incontinence and had to use incontinence pants on a regular daily basis.
At home one would dispose of used incontinence pants in the normal rubbish disposal bins - in a hotel the only place to put such items would likely be in a small bin in the bathroom which possibly would not be big enough and the person concerned might be embarrassed to leave them for the person cleaning the room to deal with.
I suggest therefore that PB may have made a daily trip to a nearby rubbish bin in the streets to dispose of his used incontinence pants. From the CCTV pictures the purple bags appear to contain something soft, (no sharp edges).
If, as we are led to believe, he made at least 13 trips with the bags, the sheer volume of the contents of that many bags would exceed what he brought into the hotel in his hold-all. The pants when dry and unused would of course have a much smaller volume than when wet and used, so possibly there was sufficient room in the hold-all when they were unused.
It is assumed that he had no passport with him but this is based on the fact that he was not asked to show one when he checked in. His passport could have been in the computer bag all along and he did also take that bag with him to Rosses Beach where it disappeared.
Interestingly he had a purple bag with him on his last day at Rosses Beach which could have been his supply of dry pants for that day.
When the police searched the local bins they were looking for his “person possessions” - used incontinence pants would I suspect not have drawn any attention.