Going by the footprints left at the scene, it appeared more than one person had been involved in the break-in.
The burglars used a brick to smash a louvre window and - despite the alarm going off - climbed inside and helped themselves.
Some of the stolen items would have formed part of the 235 Christmas hampers the Salvation Army was preparing to give out to needy families in December, Mr Mullenger said.
"What frustrates us is that this is food we give out daily. They are stealing from their neighbours, so to speak, taking food from those that we try and help.
"This [theft] just means that we can't assist families with the depth that we'd like to. My annual budget is $15,000 but we gave out over $300,000 worth of stuff if you go and buy them," Mr Mullenger said.
"We'll just work harder and door tap for more donations."
The Salvation Army's Bridge Programme office on Alexander St was also broken into on Sunday evening but nothing was stolen.
Mr Mullenger has urged the public to donate items such as baby food, nappies, cans of fruit and tinned vegetables, if they wish to help.
Constable Paul Overton said police were following strong leads.