The move follows research which shows some children as young as 10 regularly leave school premises to buy unhealthy snacks and fizzy drinks.
In addition to the health issues involved, education bosses also fear the pupils could be injured or killed in a road accident.
In 2009, the city council introduced the 'Big Eat In' in eight secondary schools which encouraged S1 pupils to stay in school at lunchtime and eat healthily.
The scheme proved so successful it has now been adopted by more than half the city's 30 secondaries.
It involved setting up a 300 metre exclusion zone round the schools in a bid to discourage pupils buying unhealthy food from vans.
Recent research was carried out around five secondaries to identify shops selling food to pupils.
They found between five and 30 outlets, many using marketing ploys to entice the pupils to buy.
Council staff bought 45 products and checked them for their nutritional quality.
A report to go before councillors next week states: "The sample of foods analysed were found to be of very poor nutritional quality."
Cordia, a council arm's-length organisation, supplies city schools with lunchtime meals.
Next week Glasgow City Councillors will be asked to consider banning all primary pupils leaving school at lunchtime unless they have their parents' express permission.