All that meat and no potatoes...
The choices for carbohydrate filler are effectively four:
though you can add a fifth as pre-cooked and dried chana dal. This last, though I'd normally dry mixed in with its curry.
If you're wanting to save on volume, there are really only three pasta to consider, balled egg noodles, macaroni, and risoni, the last a small pasta shaped like large grains of rice. Just about all other pasta occupies at least twice the volume of an equivalent weight of these three. Typical cooking time, though, is 8-10 minutes, after you've already brought the water to the boil, and they need quite a lot of water and a large billy to avoid being a gluey mess, and that's expensive in gas.
You might consider these a valid option on the Great Walks where gas and cookers are supplied as well as a bunch of larger garage sale aluminium cooking pots.
Couscous and pre-cooked rice have the advantage that all they need is an approximate equal volume of boiling water poured over them and they are then left to sit for ten minutes while they soak it all up. Weight-wise, like pasta, both are heavy compared with instant mashed potatoes, and you need to check with all concerned beforehand as couscous is not a universal favourite, even in its flavoured forms.
Instant mashed potatoes have one disadvantage. They taste like shredded Weetbix packets. But they are pre-cooked, light, low volume, and absorb enormous quantities of water, and they go well with most of my mince dishes, especially once Miranda invented various ways to add interest. (OK, if you need to chew hard on SOMETHING, pull out a couple of pieces of biltong.)
You can add various dried vegetables, especially finely chopped dried tomato; you can add (a little) powdered parmesan, you can add a touch of Maggi chicken stock.
Basically you're following the packet instructions carefully regarding how much liquid to add and how to do it. There's just a few extras to consider.
There will be some water available after cooking the Surprise peas, beans or what have you. Use the vegetable water, for a start, plus as much extra water as you need beyond that to make up the required amount.
Use a knob of butter - or take a little ghee, if you're tramping for several days in hot weather, and add a little instant trim milk powder, and a little flaked dried onion - available from Bin Inn and such like bulk food stores, all before you add the liquid.
If you're adding dried vegetables to the mix, you might like to put them on to soak at the same time as the main meal, and perhaps cook them a little in the Surprise water before finally adding them to the mix just before serving.
Experiment with chicken stock. If overdone it can make the whole business too rich, and part of the carbohydrate's job is to be a foil for the main meat component, not a competitor. But it can add a touch of variety.
Dave's Dried Rice
For 4 servings
Put the kettle on to boil. In a heavy base pan put two cups of long grain rice and a teaspoon of salt. No oil, though I would use a couple of tablespoons if I was eating the rice immediately. As the pan heats up, the rice will begin to turn opaque. Stir constantly to make certain it does not go brown.
When the water has boiled, turn the rice to LOW setting, add 3 cups of boiling water, and cover the pan with a close-fitting lid. Set the oven timer for 20 minutes, by which time all of the water should have been absorbed and the rice should be dry and fluffy. Spread it loosely around on a mesh sheet on as many drying trays as it takes, set the drier to 55, and leave for about 5-8 hours.
The finished product will look much the same as uncooked rice - slightly shinier, perhaps - and weigh much the same. But to prepare it for eating, all you do is pour an equal volume of boiling water over it and leave it for ten minutes. Done.
As an additional possibility, consider adding a couple of teaspoons of Maggi chicken or vegetable stock to the rice when you add the boiling water. Or you can do this at reconstituting time. Or you can use the cooking water from the Surprise vegetables to add to the rice.
If weight is a consideration, I'd take no more than one night's rice, but it's certainly easiest of all to prepare on a tramp.