An elderly poppy-day collector was "traumatised" after a young man came up to her outside New World on Thursday and snatched the donation bucket, which carried about $300.
Someone had "whipped the collection box away and took off," an angry Wanganui RSA vice-president Ted Morris said.
The incident happened just after 1pm and left the collector shaken but unhurt, he said.
"We collect it for welfare for people who belong to the RSA."
Mr Morris said the money went to things such as hearing aids, glasses and transport to Wellington hospital.
He couldn't remember anything like that happening when he was involved with collecting.
"That kid - he was a young man - his grandfather could have been killed in the war. He might even be still alive and suffering for some reason and the money could have been going to him."
Mr Morris said there were "a couple of guys" who would like to find the thief.