What sort of BBQ do you have? Will you have a camp oven and fire?
Last camping trip, self saucing chocolate puddings were a hit. The kids from a neighboring camp site came over to share too LOL.
I used a recipe from the Australian Women's Weekly so I'm sure you could google the quantities. I pre measured and sifted the dry ingredients into a ziplock bag. Same for the dry sauce ingredients. I measured out the butter into another bag. Some UHT milk in those small cartons (we don't use much milk elsewhere), and some eggs are all that's needed. Mix the pudding in a bowl with a fork or whisk, sprinkle over the sauce ingredients, top with water and bake.
Our BBQ has a hood so we can bake in it easily. I have also used the cam oven which is good because you can put coals on the lid so you get the heat from above too.