When my son was that age he loved his "magazine pictures". Since we are all about to get swamped with holiday advertising, it would be an easy activity to try.
We would look through all our magazines and catalogues and cut out interesting pictures. He kept a huge collection of them in a box. Then he'd play with them by making up stories about the pictures.
Yes! This was a favorite activity for my DS as well. He particularly enjoyed looking for different household items within furniture catalogs. We had fun cutting and pasting into a little composition book.
DS also enjoyed taking apart any household item he could get his hands on (to my great annoyance!). So I gave him a box that contained a clean spray bottle, soap dispenser, mechanical pencil with no lead, and bottles with different types of lids.
When DS outgrew those wooden chunky puzzles, I extended their use by doing hide-and-seek (ie "The sheep piece is somewhere in the dining room, the rooster piece is under a sofa cushion, can you find them and put them in the puzzle?", etc). This activity can be entertaining for a surprisingly long period of time.
This is sort of quirky, but I buy two identical packs of postcards featuring my favorite artists and use them to do matching and memory games.
I haven't done this since my second came along, but I used to make bread dough in clear, 6 quart storage containers -- it was fun to watch the dry and wet ingredients mix into dough and then to watch the dough rise. We just used those super-easy, Bread in 5 minutes a day recipes.
Here's another trick: I noticed that if I put on some background music, like classical, that is stimulating enough that DS will play with toys that he is usually bored with.
