Lego.
Garden tools, seeds and bulbs, etc.
Sand and a tray. A bunch of different jugs and pots and funnels -- these can be used with the sand, or in the bath, or you can nail them to an outside fence to make a water chute.
Blackboard paint on a door and chalk.
Cooking.
A good magnifying lens; later decent binoculars; a robust microscope; later a decent telescope. And stuff to look at.
Playdough, both commercial and homemade.
In the UK local councils have industrial recycling facilities where they separate out a bunch of stuff that can be used for craft project. So, for example, you can find industrial sized bobbins of different shapes and sizes; fabric off cuts; some mis-shapen spectacle lenses; weird bits of plastic; etc etc. You turn up, pile stuff in a box and pay a small sum for it. You then make stuff from it. (We made fake binoculars and a race car.)
There's a bunch of sensory stuff that I thought my child would like, but it turns out I like them much more. EG: a glitter bottle. You take an empty plastic soda bottle, half fill it with clear glue, add a bunch of glitter (restrict it to two or three colours) and add a few drops of food colour. Top it up with clean water. Seal the top. Shake very well.
The theme here is fuck commercial toys. Imagination and time is what makes the difference.
I'm just starting to build forts with my own kids. They are excited about it, but not as excited as, say, playing video games. It's kind of weird, but I hardly see any kids making forts any more. In ten years or so I've seen maybe one place that would qualify as a fort. Nothing like when I was a kid.
No other teacher ever gave me any problems which needed that kind of power at the time, so I just played. I learned so much.
Another big one, but one that I don't see often, is Capsela (http://www.wikiwand.com/en/Capsela). I loved the fact that it actually moved and did stuff and could roll or float.
Nowadays, if I were a kid, I'd probably play with one of the programmable Lego sets until it broke or broke something else!
Made lots of models, primarily fighter jets (F-14, F-15, F-16, F-18) but also a lot of Star Trek ships (a large 1701-D was my baby). Lego as well...
Also had a decent microscope and chemistry sets.
Teach your kids to make things and explore.
Toys: Whatever I had would be dwarfed by any smartphone available today or even a Raspberry Pi.
Life Experiences: Doing my own (tiny kid-style) startup.