A simple little game that's been used at all sorts of parties.  Fill a jar with several small items.  Have guests guess how
many are in the jar.  Can have the goodie filled jar be the prize.  Closest guess wins.  Easy to customize.
Ideas: Candy is always easy.  Use colors that go with theme.
Baby Shower: bath beads, q-tips, safety pins, cotton balls, pastel mints,
Birthday: balloons, pennies (pirate theme), marbles, plastic dinos, nuts, jewelry kit*
Easter: jelly beans, mini marshmallows
Halloween: candy corn, spider rings, orange paper pumpkins, plastic bugs
St. Patrick's Day: green gum drops, green paper clovers
Thanksgiving: feathers, nuts
Valentine's Day: pink red & white paper hearts

* See linking page.  Include string & a cute label.
"When a man retires, his wife gets
twice the husband but only half the
income."