I took a wrap from a X-Country train

The notable issue is the amount of CO₂ produced relative to the calories (Kcal) available.

The CO₂ is 0.59Kg so for arguments sake I will round this to 0.6Kg or 600 grammes.

The Calories are listed as 409 so let's say 416 per 600 of CO₂ or 4 calories per 6 grammes of CO₂. 4 calories are that obtained from 1gramme of protein or carbs. Fat does provide more Cal per gramme but not a significant issue in this.

So for 1 gramme of food is results in 6g of CO₂, and this is for a 'vegan' wrap.
The figures can be adjusted for other reasons.

CO₂ is 1 carbon and 2 oxygen molecules and the weight is spread so that approx 25% is carbon. So 1g carbon is released into the atmosphere to produce 1g of carbohydrates for example.

In a simple case of sugar ......