A trailer full of air
Recycling 80 or so of the now-empty cans of fizzy water I bought a few weeks ago, plus a couple of bags of plastic clamshells and 3-4 beer bottles. Almost the most bulky load I’ve ever carried on the yak, but also almost the lightest load.
(shopping content: I bought a single tomato after I finished dumping all of the recycling into the cans for kids bin.)