Take snacks and hot chocolate as we did, the odd cuppa soup wouldnt go a miss too especially if you have picky kids as the availability of food is minimal after meal times(all food was beautiful) except for finnish mars bars at 1.50 e a pop.
plenty cards and cluedo scrabble and jenga available for after dinner, my 2 found their ds very useful as there is obviously no tv computer access. and evenings are long, but you will find the kids are shattered!
you really dont need clothes. every imaginable layer is provided, gloves, hats, shoes, just take your own thermals and plenty of big socks, and disposable hand warmers were useful too. no one dresses for dinner, the clothes you arrived in are enough.
Ruka is very expensive is hire the equipment and have a lesson for the day, at least 400e for a family of 4 before your lunch, if you love downhill skiing great but be warned,