Google is generally pretty good about managing multiple accounts but sometimes you get completely stuck. One example is Google Inbox where your primary account is Google Apps for Work without Inbox enabled. You just get a screen saying that Inbox needs to be activated and no option to switch to another account.
There is a fix, and this sometimes works for other products as well. In the URL (https://inbox.google.com/u/0/) there is a user number. Change the 0 to 1 (or maybe 2, 3, etc depending on the number of accounts) and you can get Inbox up and running again.
One case I haven't found a clean workaround for is importing a segment or custom report in Google Analytics. You just get the default profile and if it's not what you're after then there is no way to switch. What does work here is launching an incognito window, signing in to the relevant account and then using the import link. A bit painful but gets the job done.