What kind of dough staple is easiest to make, for soaking in mussel juices? No oven, eggs, milk
In the southern US, people make what is known as flour bread. (Also known as biscuit bread or skillet bread.) It's made with biscuit dough that is flattened into a circle about 1/2" thick. It is cooked on top of the stove, in a lightly greased skillet over medium-high heat on one side until that side is golden brown and then flipped and cooked until golden on the other side.

I typically use leftover biscuit dough that has been shaped into a ball, wrapped and refrigerated overnight. (It doesn't have to be leftover but I do find that the time in the fridge makes a difference.)

Typical southern-style biscuits are made with flour, salt, hard fat (vegetable shortening or lard), baking powder, and water or milk (cook's choice). So, no need for milk, eggs, or an oven.

It's great for sopping up gravy or juices.