First time Cruiser; going to Alaska on Celebrity Solstice

Can the beverage packages be bought for some but not all in a cabin?

Best excursions for an elderly person with a walker or wheelchair?

any other advice for a newbie

Beverage package: Yes it can be bought for some but not all.

Excursions: Choose gentle excursions that do not require physical exertion. This should help:

http://www.newmobility.com/2014/03/cruising-alaska-wheelchair/

and here are some shore excursions for disabled:

http://www.disabledcruiseclub.com/about/alaska-shore-excursions.html

I would suggest the Lumberjack show in Ketchikan, White Pass railroad.

Celebrity offers some accessible shore excursions and you can request information on these here:

http://www.celebritycruises.com/onboard-celebrity/cruise-activities-accessible-excursions#onboard_mobility_disabilities_tab/onboard-celebrity/cruise-activities-mobile-disabilities?subtab=true