Some great, easy activities are setting up a treasure hunt around the house with clues that are pictures (for those who can't read yet) leading to a small prize at the end - an exciting conclusion keeps them engaged throughout!
Another favourite of mine is creating a sensory bin with some favourite toys and filling it with various materials like rice, pasta, or beans for them to explore. You can also theme these with different colours/ scents to make it even more exciting and tie it into learning about seasons or nature!
For some good fine motor skill practice, I often get out the baking tray with some shallow water and floating toys - a fun, simple set up that's easy to clear away afterwards too. My toddlers also love helping me cook, especially making anything with rolling pins and cookie cutters - again, great for fine motor skills! Offer some safe taste tests along the way, and they're keen as mustard!
And finally, an all-time favourite that's so easy it's embarrassing - a big cardboard box, perfect for climbing in and out of, hiding behind, adding some furniture to make it a fort, or decorating it however your toddler likes. The possibilities are endless with this one!