Various royal items, a large potty holding one (7)
I believe the answer is:
regalia
'various royal items' is the definition.
'a large potty holding one' is the wordplay.
'potty' is an anagram indicator.
'holding' indicates putting letters inside.
'one' becomes 'i' (Roman numeral).
'a'+'large'='alarge'
'alarge' anagrammed gives 'regala'.
'regala' enclosing 'i' is 'REGALIA'.
(Other definitions for regalia that I've seen before include "Trappings of royalty" , "Finery" , "Crown jewels" , "Badges of office" , "Paraphernalia indicative of high office" .)