Use the Clear Collected Item(s) action when collecting from multiple App data sets or to go into the same App twice for different items in the same flow. This action can also be used to free up memory when performing multiple searches into large Apps.
Using this will allow you to hold Field Data from previously collected Items in Custom Variables and use them later on in actions without having to hold a lot of system memory.
EXAMPLE
Using the action Clear Collected Items, you can perform the Get Referenced Items on multiple relationship fields. 
Add the Get Referenced Item and set up to find the first relationship field Item to use.
Add Custom Variable and insert the referenced field token to create the Fields needed in later actions. Add as many Variables as needed.
Add the Clear Collected Items action
Repeat the above steps for each App Item(s) needed to collect, creating Variable tokens for each field required
Create the action required and use the created Variable tokens in the appropriate fields