Does anyone have any advice on how best to use this? Is it really best to make all shopping websites open in the same containers? Any thoughts on what sites/kinds of sites should definitely be in their own containers. Any recommended categories besides the default container categories?
I would have a container for each of my major social network / email accounts, like one container for each of twitter, Google and Facebook.
Yes, and then do your browsing in non-containers so that browsing is isolated from the account logins, and vice versa.
Or use the multi-account container addon: Which will get you a new container, in a new tab with 1 click.