One man was sorely missed among the nearly 15,000 people who were expected to move through the Salvation Army’s back-to-school backpack distribution by the end of the day Thursday: Ian Johnstone, the general manager of Cenex Zip Trip, who was one of the biggest supporters of the event. Johnstone died in his sleep early Wednesday morning at the age of 54. “You always heard him here before you saw him,” said Sheila Geraghty, Salvation Army business administrator. “He was boisterous and energetic, always ready to go. He is very much missed.”