Lightweight stuff ... Thule Atlantic:
Bouyancy aid jackets, cycling helmets, kayak helmets, hiking back sacks, nordic poles, waterproof barrel for boating, bicycle bardales and pannier bags, first aid kit, warning triangle, picnic blanket, some clothing etc ... i.e. mostly activity stuff.
The very light stuff: pillows/duvets/towels etc all go in a vacuum pack case and reside in the trailer.
Last time we put in the roof box the camping chairs 2 adult 2 child, water carrier, wind breaker, kids scooters, camping stove, fishing nets for the kids, kids ready beds, and quite a few other bits, with plenty of space left as the boot had the tent, duvet, box with kitchen stuff/food etc and our suitcase.
We need to pack better than last time for our next trip as we are taking the dog too so need more boot space.
Can't remember how many litres our box is, but we fit loads in - again, mostly the lighter bulky stuff, chairs, duevts, airbeds etc.
And an absolute bargain as only paid £20 on ebay for it. Mind you the roofbars and fittings cost another £100.
Have to say though, worth every penny - we just couldn't fit everything in without it.
We used our halfords one I bought off Ebay for 40 including the roof bars for the 1st time last week.
Its great, we have 4 big folding chairs, air beds, small stove, wind break, 2xl sleeping bags and 2 single bags, 2 liners and a few extra bits and pieces. I've left it all in the car for when we go again next Monday ;-)
Amazing family weekend with old steam engines, classic car displays, market stalls, and full catering and bar. And camping on site - Save £25 by booking in advance.