No.1 Ceremonial
Uniform
White tunic. Formal occasions: parades &
ceremonies, commissioning, and even funerals. All ranks, both
genders. Pants for females.
No.2 Mess Kit
This is worn during cocktails,
mess dinners or evening functions. Red bow tie. Functions where
male civilians wear tuxedos and female civilians wear
evening gown.
No.3 Service Uniform
Worn in less formal
functions, where civilians wear short sleeves open neck. Of cause,
for clerks and appointed administration staffs too.
No.4 Uniform
As we all
already know. I think RSAF and RSN
has coveralls for No.4
No.5T
"Modified" version of No.3 Service
Uniform. Extended full long sleeves worn with a tie.
During formal functions with civilians who will be wearing shirt
and tie or lounge suit.
No.5J
Coat and tie functions. Most oftenly
worn by the ADCs (Aides-de-Camp) and Honorary ADCs. Also for
formal functions like PM Swearing-In etc.
No.5J (Enhanced)
All of No.5J with
the addition of full service medals on the bush
jacket
Best of knowledge. 
Correct me if any.