Octopus: yes; by default they cost $150 which is $50 deposit and $100 value; that's probably enough, you can top up at any MTR/7-Eleven if necessary. Don't use the Octopus for the Airport Express - buy separate group tickets for that.
Carbine Club: how can you be confirmed at a lunch that you don't know the location of?
Spas: what's your budget? (acceptable answers being HK$500-HK$5000 or so)
Cable car: do you mean the Peak Tram or the Ngong Ping360?
Rugby: if you're a kid (or a kid at heart) then it's best in the South Stand, but you'll need to be there VERY early to get a seat there; otherwise it's best in a corporate box. Without that then no specific tips.
Restaurants: cuisine? budget? HK has very many restaurants!