Essential items named before marriage (introductions to dating sites) (5)
I believe the answer is:
needs
'essential items' is the definition.
(a need is something essential)
'named before marriage introductions to dating sites' is the wordplay.
'named before marriage' becomes 'nee' (nee may be written to show someone's name at birth).
'introductions to' indicates taking the first letters.
The initial letters of 'dating sites' is 'ds'.
'nee'+'ds'='NEEDS'
(Other definitions for needs that I've seen before include "Can't do without" , "What is required" , "Essentials" , "'..... must when the devil drives'" , "Requirements" .)