FolkboatM26 said..
Any ideas where to get 5kg block ice these days (Sydney, inner west)? Back in the day could get from lots of servos, now cannot find. Tried lidcombe ice out at sefton who sell it, but too great a hike.... trying to get a bit more sustained refrigeration.
No idea

I freeze 20 L tub plus lots of marge containers to take fishing, camping.
Have you thought of dry ice from Boc ?
Just found some tips
www.snowys.com.au/blog/tips-for-keeping-ice-longer-in-your-icebox/