Some moms do goodie bags and that's fun but definitely not required. Some ideas from Valentine's day past:
Little goody bag with a few pieces of candy and a toy tied with a ribbon and a store-bought card as a tag. We found the toys at the party store in the birthday aisle. I think we put in a heart-shaped balloon and a little kaleidoscope that came in packs of 8.
heart-shaped suckers with a tag and curly ribbon
store-bought cards with a piece of taffy or candy attached
Homemade hearts made out of construction paper
Light sticks (left over from Halloween) with a tag and a ribbon