Hi Wendy,
Up to you since you've 'worked' the whole day & the dinner is a reward. but i think should still give something to help cover the cost of the dinner.
some people put back the money that they receive from the bride/groom's ang bao to them - meaning that they're not doing it for money.
if you know that the bride/groom very stingy and won't give you anything, then don't need to give ang bao - just take the dinner as your gift. *)