Far more than you think you will need, so you always have something to pull out of the bag.
I'd do activities as well as games, so some crafts (decorate a handled paper bag as first craft to keep all other crafts/winnings in) make a bracelet - pipe cleaners and pony beads, or animals out of pipe cleaners. Paper plate masks, ice a biscuit (rich tea, glance icing, sprinkles and sweets), colouring in (plenty of free pages to print online).
Team games/races - balloon over the head/under the legs - person at back run to front and start again. Pass orange down the line from under the chin - person at back run to front and start again as before. Pass balloon between the knees - can just do this passing down the line or waddle a race before passing on. Targets - circles on floor and bean bags child 1 throw bag I to circle 1, child 2 throw bag into circle 2 etc (have to retrieve and try again from the base line if they miss, child 2 can't try until 1 is successful). Once each circle has a beanbag in children retrieve bags one at a time - child 1 swaps to back of the line and repeat, so by the end of the race each child has had to aim for each circle.
Party participation games - hokey cokey, heads and shoulders etc, with say the Macarena, Baby Shark, Agadoo, and some general dancing. If you have a bubble machine on during the general dancing this goes down very well!
Musical chairs, statues, islands (newspaper) Simon says.
Rather than a treasure hunt for sweets, do a pairs treasure hunt. Get a load of old birthday or Christmas cards, and cut the picture in half. Hide one half, and give each child or team one of the remaining halves - once they find the picture match they bring it back to you for another half. Team with most pairs at the end wins. (could also use a pairs game for this, or even 2 packs of cards, but these can look a bit too similar for little ones)