Extended Events: Specify Session Data Storage left blank
If you specify no target, but choose to use an Extended Events wizard template for the the session, it is created with a single histogram target.

You can see this by clicking through to the last page of the wizard, then hitting the "script" button.

This is a sample I created using the "script" button.  Below this is one where I specified a ring buffer as a target:

CREATE EVENT SESSION [test] ON SERVER 
ADD EVENT sqlserver.additional_memory_grant,
ADD EVENT sqlserver.lock_acquired(
    ACTION(sqlserver.query_hash)
    WHERE (([package0].[greater_than_uint64]([database_id],(4))) AND ([package0].[equal_boolean]([sqlserver].[is_system],(0)))))
ADD TARGET package0.histogram(SET filtering_event_name=N'sqlserver.lock_acquired',source=N'sqlserver.query_hash')
WITH (MAX_MEMORY=4096 KB,EVENT_RETENTION_MODE=ALLOW_SINGLE_EVENT_LOSS,MAX_DISPATCH_LATENCY=30 SECONDS,MAX_EVENT_SIZE=0 KB,MEMORY_PARTITION_MODE=NONE,TRACK_CAUSALITY=ON,STARTUP_STATE=OFF)
GO


This is the one with the ring-buffer:

CREATE EVENT SESSION [asdf] ON SERVER 
ADD EVENT sqlserver.additional_memory_grant,
ADD EVENT sqlserver.lock_acquired(
    ACTION(sqlserver.query_hash)
    WHERE (([package0].[greater_than_uint64]([database_id],(4))) AND ([package0].[equal_boolean]([sqlserver].[is_system],(0)))))
ADD TARGET package0.histogram(SET filtering_event_name=N'sqlserver.lock_acquired',source=N'sqlserver.query_hash'),
ADD TARGET package0.ring_buffer
WITH (MAX_MEMORY=4096 KB,EVENT_RETENTION_MODE=ALLOW_SINGLE_EVENT_LOSS,MAX_DISPATCH_LATENCY=30 SECONDS,MAX_EVENT_SIZE=0 KB,MEMORY_PARTITION_MODE=NONE,TRACK_CAUSALITY=ON,STARTUP_STATE=OFF)
GO


As you can see above, the only difference is the lack of a ring-buffer target in the first result, even though they bot have a histogram target.

However, if you do not use a template when building the Extended Events session, the session is created like so (I just added a single event and action):

CREATE EVENT SESSION [test] ON SERVER 
ADD EVENT sqlserver.additional_memory_grant(
    ACTION(sqlserver.client_pid))
WITH (STARTUP_STATE=OFF)
GO


This results in the session only providing live data, which is viewable via the "Watch Live Data" context-menu of the XE Session:



You can obtain a live stream of the rows returned by the Extended Event by looking at the very lightly documented system function, fn_MSxe_read_event_stream function, as in:

DECLARE @source nvarchar(256);
DECLARE @sourceopt int;
SET @source = N'test';
SET @sourceopt = 0;

SELECT xes.type
    , CONVERT(xml, CONVERT(varbinary(max), xes.data))
FROM sys.fn_MSxe_read_event_stream(@source, @sourceopt) xes


However, the format of the data returned is image, and apparently "not customer readable".