I agree with OTD. Low GI carbs will help keep you feeling full for longer. Also consider adding more protein to your diet. You're doing a lot of heavy lifting so you want to make sure your muscles have plenty of protein to repair themselves! Protein also helps keep you full for longer.
You could try mixing some low-cal tinned tuna with pasta. To make pasta lower in GI, cook it then cool it. It changes the chemical structure so that it releases its sugars more slowly into the blood. Same with potatoes.
Multigrain bread, as OTD pointed out, is much better for keeping you full than white bread. Rather than vegemite and margarine, add something with more nutrients. Salad with a low-fat ham, or low-fat cheese will fill you up. And rather than spreading it with margarine, use something slightly lower in fat that will add nutrients. Hommus, relish or even mashed up avocado are good alternatives.
The site that this weight loss forum is a part of has a list of healthy lunch recipes
. You might consider selecting some options from there.