Our family (2 adults and 3 kids - aged 15, 18 & 20) flew JAL to Japan in 2006.
We had clothes, 5 pairs of ski/snowboard boots plus 4 sets of skis and 1 snowboard for 3 weeks. Every item was weighed at each check-in (SYD, KIX, CTS & NRT) and added together but we were able to remain below 100kg total.
We achieved this in the following way:
We each carried a day pack with our own toiletry bag, one ski boot, helmet (so it didn't get damaged), gloves, goggles, reading material, camera etc plus our ski jacket over our arm.
Each family member was only allowed one pair of shoes/boots (this turned out to be sufficent as the snow in Japan is so dry that nothing gets wet), 1 pair ski pants, 2 pairs of jeans/pants, various tops/windstopper and the ski jackets doubled as going out jackets. Thermals kept us warm when we were skiing and also when we were sightseeing and it was easy to manage 3 suitcases and 2 ski & snowboard bags between us. I organised all ground transport (trains & buses) independantly and we didn't ever have a problem lugging our stuff up and down stairs, along streets and onto trains.
Not once did anyone complain that they didn't have enough clothes!
Happy skiing!!!