We have done bush walking. Swimming after lessons (then I only have to pay for me).
Bike riding.
Movie nights at home.
Camping in the lounge room.
Gardening (aka weeding).
Library trips - the activities there aren't free and book up as soon as the list is out tho so just visits.
Playdates at the park, pool, friends houses. Bring our own food and water.
Washing and pegging clothes etc, they love to help.