We often found a lot of things on the enchanted learning site last year when dd was 3 going on 4
http://www.enchantedlearning.com/crafts/toddler/
http://www.first-school.ws/theme/seasons_summer.htm (another one we picked ideas up from)
I think a lot of things at this age depend on individual abilities, interests and how long they want to spend on an activity. Thinking back over the last year or so, these are some of the things we’ve enjoyed.
I know you like crafting so is he able to do some simple sewing projects? Finger knitting and weaving maybe? Weaving with wool and then natural things found on walks or in the garden - flowers, grasses, twigs, etc. Some wet felting might be fun - either felt balls and then make stuff from them or making felt sheets - rainbows or pictures. Making friendship braids is always fun with little ones, boys and girls, we do this a lot in the Summer months with the weaving guild I’m a member of at events.
Clay modeling, perhaps decorated with shells and things picked up on walks or at the beach.
Sun catchers with tissue paper or coloured cellophane.
Making simple puppets either paper and card or some felt and other fabric and put on a puppet show. Clothespin dolls or wooden spoon dolls, again could do a puppet style show or storytelling.
hope some of these give you some ideas.