Wear the bulkier items on board? It's a bit of a pain, but if you are capacity limited, needs be done.

(Fieldwork in Korea in the winter was just miserable. Multiple layers of clothing, boots, high vis, telescope and tripod, fleece and waterproofs - at least I didn't need a hard hat on that one. And all travelling in Y with a 23 kg limit - although I did have a 40 kg limit due to holding status - but I also couldn't manage more than one bag, so could only carry approx 30 kg - 3 bags?! you were lucky )