Buckets I used to use were old ready-mixed adhesive buckets most of the time. It can be handy to get a mixing bucket from an adhesive manufacturer though (via a
tile store usually) as when you're mixing leveling compounds and such-like it has the water levels marked on the bucket for you.
The 'whisk' or padle mixer usually does just fit in a drill. Although you can also get paddle mixers which are dedicated mixing machines which have a decent speed control setting or trigger and good handles for those thick mixes (to stop it spinning out of your hands).
Obviously the bags of adhesive will always say how much water is needed or if a bottle of polymer/admix is required etc.
I always start with a bit of water in the bottom of the bucket and mix a little adhesive before adding lots more water and more powder to ge the required amount... seems to get less lumps, maybe its just an old habbit though. Aways mix less than you need and add to it, as you can never mix too much and take some back as they say.