My 4 year old son has a swimming lesson on Saturday morning. He likes the spend the afternoon riding his bike round the village (with me running after him with my toddler on his pushalone trike). He enjoys anything outdoors - football, running around aimlessly etc. He also loves cooking and will happily spend 2 hours with me making cakes etc.
Recently he has got very much into arts and crafts. Tomorrow his school is on strike so we are going to spend the day making hand made decorations. He loves drawing, cutting, sticking etc.
He loves dressing up and role play. We often all play shops, priates, police etc. - whatever he demands we pretend to be. If I paint his face in the morning, he stays in character all day long.
On Sundays we normally have a family day out to the zoo or country park etc. We have season tickets to about 3 places so rotate which ones we go to. When I have worn him out (which takes a LOT), I get to go riding!