There are several date&time functions that dont need any items to be calculated: 

now()

time()

date()

dayofmonth()

dayofweek()**

Will be very good if this functions can be used in trigger expressions and calculated items "as is", i.e, for example:
simply now()
instead of:
{template_name:item_key.now()} - in trigger expression
or 
now(item_key) - in calculated item expression
This is boring and annoying - to escape special characters and doing other strange work to get simply current unix_timestamp on the server.