I have a 27 month old and have the same frustrations with what am I going to do each day. Here are a few thing we've done:
1. I get a baking tray (the deepest one you have) and give small plastic cups, sponge, old spice/seasoning containers, spoons, and let my son pour and play with water. If you want to get messy: add corn starch to make gloop or just add flour to make some dough to play with.
2. Freezing. Fill up a deep baking tray, put in some cars, plastic small insect toys, or anything you want, and leave it outside to freeze. Let your son use a plastic hammer to get the toys out. I save a lot of cardboard milk cartons and empty plastic containers. I fill them up and freeze them outside and then my son takes a bath with them. He loves to watch it melt. Muffin tins are good too. Put in some fruit like blueberries and your son can eat them when he finds them. We count ice cubes, freeze juice, etc.
3. A set of cardboard blocks has been so helpful for us. We build it up real tall and my son uses a plastic hammer to knock it over. We build tunnels for cars and trains too. There so much you can do.
4. Productiveparenting.com has some good ideas as well. It's all divided up by age.
5. Bring the snow inside. Fill up a big plastic tub with snow and let him use some kitchen utensils (big spoons, spatulas, etc) to scoop. I do this at our kitchen table and spread around a lot of towels on the floor, but we've also just taken the snow to the bathtub.
Have fun! Come on, spring! Hurry up!