Seven refillable containers: 1 x 4 oz. (120 mL), 2 x 2 oz. (60 mL), 2 x 1 oz. (30 mL), 2 x 0.5 oz. (15 mL). Polyethylene bottles with polypropylene lids. Caps are interchangeable, and some have a flip-up spout.

Decanting is how you stop carrying three pounds of packaging. A full bottle of shampoo, a full bottle of washing-up liquid and a full bottle of sunscreen weigh more than everything else in a wash bag put together, and you will use a fraction of each.

Seven bottles in four sizes covers it: shampoo and soap in the big ones, sunscreen and insect repellent in the middles, and the half-ounces for the things you need a drop of — oil, contact solution, hot sauce.

Interchangeable caps are the detail that makes the set work. Put the spout where you need to pour, the plain cap where you need it sealed, and swap them when the trip changes.

Also the right answer for air travel, where the limits are per-container.