Hastings District Council's Opera House and arts precinct subcommittee chairman Malcolm Dixon said the discoveries helped tell the history of the century-old building.
"Looking at them, you can just imagine someone holding up the boxing card for the next round; someone hanging the coming attraction sign out the front of the building - or a chap out the back in charge of set changes having a sneaky cigarette. That must have been risky with things like sets and stage drapes around."
He said it was not uncommon for a "building of this age."
Council's facilities and programmes group manager Alison Banks said artefacts found during the work would be showcased within the finished building once the project was completed.
About 400 cubic metres of concrete is expected to be poured into the Opera House within the next six months - using 150 concrete trucks.
The $11.1 million earthquake strengthening of the Opera House started on August 2 and is expected to take 20 to 24 months.