One of the places we make sure to visit when we are in the US is craft stores. I think it is important to keep a variety of craft supplies freely accessible to the kids. We've done this since they were tiny, less than 18mos. Brian was safe with things, Honor had some lessons on scrubbing crayons off walls at an early age - not her doing the scrubbing, she thought that was fun too(!), but we 'took mom away' to clean up her mess. She learned that if she wanted me, on demand, she couldn't color on the walls or I'd have to go clean. (It worked)
Some basic supplies, always on hand, are paper, crayons, markers, watercolor supplies, scissors, and glue. We sometimes have significant messes, but that's part of the learning process. I also have let the kids have yarn, beads, and some materials. When we visit the crafts stores, we always pick up a handful of kits to do as supervised projects too.
One craft/toy/activity we picked up this year was a couple of simple "Dinosaur Dig" sets. I cannot find a photo online of the kit. It's not one of the more complex sets where you have to dig out a whole skeleton and then assemble the dinosaur (maybe next year), it's more like this mystery rock set. There's a 'rock' with a toy dinosaur embedded inside it, and a tool to scrape away the sand and rock to dig it out (with a reasonable amount of effort - not too hard, not too easy). This kit came with a toy dinosaur that grows when you put it in water. Brian dug his dinosaur out carefully. Took two days. Honor saw him working on the 2nd day, and started on hers - like crazy! Sand and bits flying everywhere! (Might be best to do this as an outside activity if possible.) Soon, both dinosaurs were free, and they were asking for something to soak them in.
I cut up plastic bottles to use, but then the kids ran off. They came back with their notebooks. Brian said they needed to write down their observations before they started the water experiment. They measured and described their dinosaurs. Brian wrote a whole paragraph. Even Honor wrote her notes - with some spelling help. (He is 1 inch, he is red and yellow, etc.) Finally the dinosaurs were placed in the water. I wonder if they'll remember to record their findings when the dinosaurs have grown as much as they are going to?