A concentrated, biodegradable liquid that does hands, washing up and body. The reason to buy the multi-purpose one is not minimalism for its own sake: it is that three separate bottles is the arrangement that ends with none of them in the box.
The Food Standards Agency is clear that soap is the active part of handwashing and that temperature helps:
You can use cold water to wash your hands, as this will still clean them, however, using warm water is better
the soap/detergent lathers up more, which makes it more effective at removing bacteria
That is worth knowing in a van, because warm water costs fuel and the honest answer is that it is worth the thirty seconds on the stove before handling food.
Biodegradable does not mean “fine to use in a stream”. It means it breaks down in soil, given soil to break down in. Washing directly in a watercourse puts detergent and food residue straight into it whatever the label says. Carry water away from the source, wash, and scatter the waste water well away from it and from anywhere anyone draws from. Related: water sourcing and treatment.
Buy concentrate. A small bottle of concentrate outlasts several of the ready-diluted kind and takes a fraction of the space.